GitHub Actions MSYS2 Windows path

The MSYS2 GitHub Action v2.5.0 updated the path to MSYS, affecting workflows using MSYS2.

The new path is used like:

- name: Put MSYS2_MinGW64 on PATH
  # there is not yet an environment variable for this path from msys2/setup-msys2
  run: echo "${{ runner.temp }}/msys64/ucrt64/bin" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append