brew: Recent regression on sandboxed installs as root

Up until recently, root-owned homebrew worked. There appears now to be an issue where the sandboxed brew install can no longer access TLS certificates when run as the root user.

$ sudo /opt/homebrew/bin/brew install pkg-config
==> Using the sandbox
==> Downloading https://pkgconfig.freedesktop.org/releases/pkg-config-0.29.1.tar.gz

curl: (35) SSL certificate problem: Couldn't understand the server certificate format
Trying a mirror…

Compare to non-root-owned:

$ brew install --sandbox --build-from-source pkg-config
==> Using the sandbox
==> Downloading https://pkgconfig.freedesktop.org/releases/pkg-config-0.29.1.tar.gz
######################################################################## 100.0%
==> ./configure --prefix=/usr/local/Cellar/pkg-config/0.29.1_1 ...