install: Headless Xcode Command Line Tools installation failed on 10.14

We have an automated Jenkins job that sets up machines by installing Homebrew on them. It started failing recently.

Reproduction:

1. Have a fresh installation of macOS Mojave (tested with 10.14.4)
2. Run ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

Expected outcome: Homebrew installs successfully in interactive shell and non-interactive shell

Actual outcome: In interactive shell

In non-interactive shell

[2019-06-04T14:42:20.932Z] Installing homebrew
[2019-06-04T14:42:21.189Z] ==> This script will install:
[2019-06-04T14:42:21.189Z] /usr/local/bin/brew
[2019-06-04T14:42:21.189Z] /usr/local/share/doc/homebrew
[2019-06-04T14:42:21.189Z] /usr/local/share/man/man1/brew.1
[2019-06-04T14:42:21.189Z] /usr/local/share/zsh/site-functions/_brew
[2019-06-04T14:42:21.189Z] /usr/local/etc/bash_completion.d/brew
[2019-06-04T14:42:21.189Z] /usr/local/Homebrew
[2019-06-04T14:42:21.189Z] ==> The following existing directories will be made group writable:
[2019-06-04T14:42:21.189Z] /usr/local/lib
[2019-06-04T14:42:21.189Z] /usr/local/lib/pkgconfig
[2019-06-04T14:42:21.189Z] ==> The following existing directories will have their owner set to anka:
[2019-06-04T14:42:21.189Z] /usr/local/lib
[2019-06-04T14:42:21.189Z] /usr/local/lib/pkgconfig
[2019-06-04T14:42:21.189Z] ==> The following existing directories will have their group set to admin:
[2019-06-04T14:42:21.189Z] /usr/local/lib
[2019-06-04T14:42:21.189Z] /usr/local/lib/pkgconfig
[2019-06-04T14:42:21.189Z] ==> The following new directories will be created:
[2019-06-04T14:42:21.189Z] /usr/local/bin
[2019-06-04T14:42:21.189Z] /usr/local/etc
[2019-06-04T14:42:21.189Z] /usr/local/include
[2019-06-04T14:42:21.189Z] /usr/local/sbin
[2019-06-04T14:42:21.189Z] /usr/local/share
[2019-06-04T14:42:21.189Z] /usr/local/var
[2019-06-04T14:42:21.189Z] /usr/local/opt
[2019-06-04T14:42:21.189Z] /usr/local/share/zsh
[2019-06-04T14:42:21.189Z] /usr/local/share/zsh/site-functions
[2019-06-04T14:42:21.189Z] /usr/local/var/homebrew
[2019-06-04T14:42:21.189Z] /usr/local/var/homebrew/linked
[2019-06-04T14:42:21.189Z] /usr/local/Cellar
[2019-06-04T14:42:21.189Z] /usr/local/Caskroom
[2019-06-04T14:42:21.189Z] /usr/local/Homebrew
[2019-06-04T14:42:21.189Z] /usr/local/Frameworks
[2019-06-04T14:42:21.189Z] ==> The Xcode Command Line Tools will be installed.
[2019-06-04T14:42:21.189Z] ==> /usr/bin/sudo /bin/chmod u+rwx /usr/local/lib /usr/local/lib/pkgconfig
[2019-06-04T14:42:21.189Z] ==> /usr/bin/sudo /bin/chmod g+rwx /usr/local/lib /usr/local/lib/pkgconfig
[2019-06-04T14:42:21.189Z] ==> /usr/bin/sudo /usr/sbin/chown anka /usr/local/lib /usr/local/lib/pkgconfig
[2019-06-04T14:42:21.445Z] ==> /usr/bin/sudo /usr/bin/chgrp admin /usr/local/lib /usr/local/lib/pkgconfig
[2019-06-04T14:42:21.445Z] ==> /usr/bin/sudo /bin/mkdir -p /usr/local/bin /usr/local/etc /usr/local/include /usr/local/sbin /usr/local/share /usr/local/var /usr/local/opt /usr/local/share/zsh /usr/local/share/zsh/site-functions /usr/local/var/homebrew /usr/local/var/homebrew/linked /usr/local/Cellar /usr/local/Caskroom /usr/local/Homebrew /usr/local/Frameworks
[2019-06-04T14:42:21.445Z] ==> /usr/bin/sudo /bin/chmod g+rwx /usr/local/bin /usr/local/etc /usr/local/include /usr/local/sbin /usr/local/share /usr/local/var /usr/local/opt /usr/local/share/zsh /usr/local/share/zsh/site-functions /usr/local/var/homebrew /usr/local/var/homebrew/linked /usr/local/Cellar /usr/local/Caskroom /usr/local/Homebrew /usr/local/Frameworks
[2019-06-04T14:42:21.445Z] ==> /usr/bin/sudo /bin/chmod 755 /usr/local/share/zsh /usr/local/share/zsh/site-functions
[2019-06-04T14:42:21.445Z] ==> /usr/bin/sudo /usr/sbin/chown anka /usr/local/bin /usr/local/etc /usr/local/include /usr/local/sbin /usr/local/share /usr/local/var /usr/local/opt /usr/local/share/zsh /usr/local/share/zsh/site-functions /usr/local/var/homebrew /usr/local/var/homebrew/linked /usr/local/Cellar /usr/local/Caskroom /usr/local/Homebrew /usr/local/Frameworks
[2019-06-04T14:42:21.445Z] ==> /usr/bin/sudo /usr/bin/chgrp admin /usr/local/bin /usr/local/etc /usr/local/include /usr/local/sbin /usr/local/share /usr/local/var /usr/local/opt /usr/local/share/zsh /usr/local/share/zsh/site-functions /usr/local/var/homebrew /usr/local/var/homebrew/linked /usr/local/Cellar /usr/local/Caskroom /usr/local/Homebrew /usr/local/Frameworks
[2019-06-04T14:42:21.701Z] ==> /usr/bin/sudo /bin/mkdir -p /Users/anka/Library/Caches/Homebrew
[2019-06-04T14:42:21.701Z] ==> /usr/bin/sudo /bin/chmod g+rwx /Users/anka/Library/Caches/Homebrew
[2019-06-04T14:42:21.701Z] ==> /usr/bin/sudo /usr/sbin/chown anka /Users/anka/Library/Caches/Homebrew
[2019-06-04T14:42:21.701Z] ==> Searching online for the Command Line Tools
[2019-06-04T14:42:21.701Z] ==> /usr/bin/sudo /usr/bin/touch /tmp/.com.apple.dt.CommandLineTools.installondemand.in-progress
[2019-06-04T14:42:43.596Z] ==> Downloading and installing Homebrew...
[2019-06-04T14:42:43.596Z] xcode-select: note: no developer tools were found at '/Applications/Xcode.app', requesting install. Choose an option in the dialog to download the command line developer tools.
[2019-06-04T14:42:43.596Z] Failed during: git init -q
script returned exit code 1

Also, the following popup is visible on the machine:

Here is the non-interactive output from the 8th of May when it was still working correctly:

20:31:15  Installing homebrew
20:31:16  ==> This script will install:
20:31:16  /usr/local/bin/brew
20:31:16  /usr/local/share/doc/homebrew
20:31:16  /usr/local/share/man/man1/brew.1
20:31:16  /usr/local/share/zsh/site-functions/_brew
20:31:16  /usr/local/etc/bash_completion.d/brew
20:31:16  /usr/local/Homebrew
20:31:16  ==> The following existing directories will be made group writable:
20:31:16  /usr/local/lib
20:31:16  /usr/local/lib/pkgconfig
20:31:16  ==> The following existing directories will have their owner set to anka:
20:31:16  /usr/local/lib
20:31:16  /usr/local/lib/pkgconfig
20:31:16  ==> The following existing directories will have their group set to admin:
20:31:16  /usr/local/lib
20:31:16  /usr/local/lib/pkgconfig
20:31:16  ==> The following new directories will be created:
20:31:16  /usr/local/bin
20:31:16  /usr/local/etc
20:31:16  /usr/local/include
20:31:16  /usr/local/sbin
20:31:16  /usr/local/share
20:31:16  /usr/local/var
20:31:16  /usr/local/opt
20:31:16  /usr/local/share/zsh
20:31:16  /usr/local/share/zsh/site-functions
20:31:16  /usr/local/var/homebrew
20:31:16  /usr/local/var/homebrew/linked
20:31:16  /usr/local/Cellar
20:31:16  /usr/local/Caskroom
20:31:16  /usr/local/Homebrew
20:31:16  /usr/local/Frameworks
20:31:16  ==> The Xcode Command Line Tools will be installed.
20:31:16  ==> /usr/bin/sudo /bin/chmod u+rwx /usr/local/lib /usr/local/lib/pkgconfig
20:31:16  ==> /usr/bin/sudo /bin/chmod g+rwx /usr/local/lib /usr/local/lib/pkgconfig
20:31:17  ==> /usr/bin/sudo /usr/sbin/chown anka /usr/local/lib /usr/local/lib/pkgconfig
20:31:17  ==> /usr/bin/sudo /usr/bin/chgrp admin /usr/local/lib /usr/local/lib/pkgconfig
20:31:17  ==> /usr/bin/sudo /bin/mkdir -p /usr/local/bin /usr/local/etc /usr/local/include /usr/local/sbin /usr/local/share /usr/local/var /usr/local/opt /usr/local/share/zsh /usr/local/share/zsh/site-functions /usr/local/var/homebrew /usr/local/var/homebrew/linked /usr/local/Cellar /usr/local/Caskroom /usr/local/Homebrew /usr/local/Frameworks
20:31:17  ==> /usr/bin/sudo /bin/chmod g+rwx /usr/local/bin /usr/local/etc /usr/local/include /usr/local/sbin /usr/local/share /usr/local/var /usr/local/opt /usr/local/share/zsh /usr/local/share/zsh/site-functions /usr/local/var/homebrew /usr/local/var/homebrew/linked /usr/local/Cellar /usr/local/Caskroom /usr/local/Homebrew /usr/local/Frameworks
20:31:17  ==> /usr/bin/sudo /bin/chmod 755 /usr/local/share/zsh /usr/local/share/zsh/site-functions
20:31:17  ==> /usr/bin/sudo /usr/sbin/chown anka /usr/local/bin /usr/local/etc /usr/local/include /usr/local/sbin /usr/local/share /usr/local/var /usr/local/opt /usr/local/share/zsh /usr/local/share/zsh/site-functions /usr/local/var/homebrew /usr/local/var/homebrew/linked /usr/local/Cellar /usr/local/Caskroom /usr/local/Homebrew /usr/local/Frameworks
20:31:17  ==> /usr/bin/sudo /usr/bin/chgrp admin /usr/local/bin /usr/local/etc /usr/local/include /usr/local/sbin /usr/local/share /usr/local/var /usr/local/opt /usr/local/share/zsh /usr/local/share/zsh/site-functions /usr/local/var/homebrew /usr/local/var/homebrew/linked /usr/local/Cellar /usr/local/Caskroom /usr/local/Homebrew /usr/local/Frameworks
20:31:17  ==> /usr/bin/sudo /bin/mkdir -p /Users/anka/Library/Caches/Homebrew
20:31:17  ==> /usr/bin/sudo /bin/chmod g+rwx /Users/anka/Library/Caches/Homebrew
20:31:17  ==> /usr/bin/sudo /usr/sbin/chown anka /Users/anka/Library/Caches/Homebrew
20:31:17  ==> Searching online for the Command Line Tools
20:31:17  ==> /usr/bin/sudo /usr/bin/touch /tmp/.com.apple.dt.CommandLineTools.installondemand.in-progress
20:31:33  ==> Installing Command Line Tools (macOS Mojave version 10.14) for Xcode-10.2
20:31:33  ==> /usr/bin/sudo /usr/sbin/softwareupdate -i Command\ Line\ Tools\ (macOS\ Mojave\ version\ 10.14)\ for\ Xcode-10.2
20:31:33  Software Update Tool
20:31:33  
20:31:33  
20:31:37  Downloading Command Line Tools (macOS Mojave version 10.14) for Xcode
20:31:37  Downloaded Command Line Tools (macOS Mojave version 10.14) for Xcode
20:32:34  Installing Command Line Tools (macOS Mojave version 10.14) for Xcode
20:32:34  Done with Command Line Tools (macOS Mojave version 10.14) for Xcode
20:32:34  Done.
20:32:34  ==> /usr/bin/sudo /bin/rm -f /tmp/.com.apple.dt.CommandLineTools.installondemand.in-progress
20:32:34  ==> /usr/bin/sudo /usr/bin/xcode-select --switch /Library/Developer/CommandLineTools
20:32:34  ==> Downloading and installing Homebrew...
20:32:41  From https://github.com/Homebrew/brew
20:32:41   * [new branch]      master     -> origin/master
[...]
20:32:41   * [new tag]         2.1.2      -> 2.1.2
20:32:41  HEAD is now at 37f4b9264 Merge pull request #6108 from Homebrew/dependabot/bundler/docs/unicode-display_width-1.6.0
20:32:46  ==> Homebrew is run entirely by unpaid volunteers. Please consider donating:
20:32:46    https://github.com/Homebrew/brew#donations
20:32:49  ==> Tapping homebrew/core
20:32:49  Cloning into '/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core'...
20:32:56  Checking out files:  78% (3945/5007)   
[...]
Checking out files: 100% (5007/5007), done.
20:33:11  Tapped 2 commands and 4775 formulae (5,032 files, 12.4MB).
20:33:12  Already up-to-date.
20:33:12  ==> Installation successful!