rustup: rustup 1.27 fails when installing targets on Windows in GitHub Actions

Problem

As of a couple of days ago it is no longer possible to install x86_64-pc-windows-gnu in github CI. This co-incides with the new rustup release 1.27.0 fairly closely.

I don’t have Windows myself, so this is incredibly hard to debug for me (I can basically just tweak and see what happens in CI), but nothing has changed in the CI configuration on my side.

The error is:

Run rustup install --profile minimal stable && rustup default stable && rustup target add x86_64-pc-windows-gnu
info: syncing channel updates for 'stable-x86_64-pc-windows-msvc'

  stable-x86_64-pc-windows-msvc unchanged - rustc 1.76.0 (07dca489a 2024-02-04)

info: checking for self-update
info: downloading self-update
warning: tool `rust-analyzer` is already installed, remove it from `C:\Users\runneradmin\.cargo\bin`, then run `rustup update` to have rustup manage this tool.
warning: tool `rustfmt` is already installed, remove it from `C:\Users\runneradmin\.cargo\bin`, then run `rustup update` to have rustup manage this tool.
warning: tool `cargo-fmt` is already installed, remove it from `C:\Users\runneradmin\.cargo\bin`, then run `rustup update` to have rustup manage this tool.
error: invalid value 'C:\Users\runneradmin\.cargo\bin\rustup.exe' for '[+toolchain]': error: "C:\Users\runneradmin\.cargo\bin\rustup.exe" is not a valid subcommand, so it was interpreted as a toolchain name, but it is also invalid. To override the toolchain using the 'rustup +toolchain' syntax, make sure to prefix the toolchain override with a '+'

For more information, try '--help'.
Error: Process completed with exit code 1.

Here is an example where it fails: https://github.com/VorpalBlade/chezmoi_modify_manager/actions/runs/8255667914/job/22582675054

Linux and MacOS runners work just fine.

Steps

1. Run rustup install --profile minimal stable && rustup default stable && rustup target add x86_64-pc-windows-gnu in github CI on Windows

Possible Solution(s)

No response

Notes

No response

Rustup version

Run rustup --version
rustup 1.26.0 (5af9b9484 2023-04-05)
info: This is the version for the rustup toolchain manager, not the rustc compiler.

Installed toolchains

info: The currently active `rustc` version is `rustc 1.76.0 (07dca489a 2024-02-04)`
Default host: x86_64-pc-windows-msvc
rustup home:  C:\Users\runneradmin\.rustup
installed targets for active toolchain
--------------------------------------
i686-pc-windows-msvc
x86_64-pc-windows-gnu
x86_64-pc-windows-msvc
active toolchain
----------------
stable-x86_64-pc-windows-msvc (default)
rustc 1.76.0 (07dca489a 2024-02-04)