CI: tests failing on windows

[ThomasWaldmann]

Seen in the canary tests, the windows CI (PR/Merge) should also be checked:

E       ValueError: invalid literal for int() with base 10: "MSYS2 path translation is active. This can cause POSIX paths to be mangled into Windows paths in archives. Consider setting MSYS2_ARG_CONV_EXCL='*' and MSYS2_ENV_CONV_EXCL='*'. See https://www.msys2./

[hiijoshi]

I can also investigate fixing this at the CI level (e.g., MSYS2 env vars) if that is preferred.

[ThomasWaldmann]

First finish your other PRs.

[ThomasWaldmann]

Well, that fix was in the right direction, but in the end it didn't work. The canary test on win32 just failed:

https://github.com/ThomasWaldmann/borg/actions/runs/23529666171/job/68490462711