[pavelzw]

shell: pixi run pwsh -Command {0} never actually executed the script. GitHub Actions only appends .ps1 to the temporary script file if the shell command starts with pwsh. With pixi run pwsh ... the file has no extension, so pwsh -Command <file> tries to start it as a native program. execve fails with ENOEXEC and .NET falls back to shell-execute (xdg-open on Linux):

• ubuntu-latest / macOS / Windows: the step silently passes without running anything
• ubuntu-24.04-arm: no xdg-open is installed, so it fails with No such file or directory (Investigate why ubuntu-24.04-arm with pixi-shell pwsh behaves weirdly #198)

pixi run pwsh -File {0} (suggested in #78) works on Linux/macOS but fails on Windows because of the missing .ps1 extension.

Investigation and variant matrix in #304. pixi run pwsh -NoProfile -Command "Invoke-Expression (Get-Content -Raw '{0}')" works on all platforms.

Changes:

• README: recommend the working invocation
• Tests: use the working invocation, drop the ubuntu-arm skip, assert the script actually ran (marker file) and that a failing script fails the step

closes #78, closes #198, closes #304

If updating documentation:

• Updated documentation in https://github.com/prefix-dev/pixi/blob/main/docs/integration/ci/github_actions.md as well: docs: Fix PowerShell custom shell example for GitHub Actions pixi#7423