ci: Failed to save cache on windows

[jakoschiko]

The windows runner in the CI is the slowest one. Maybe it's related to this error that I saw:

Prepare all required actions
Getting action download info
Run ./.github/actions/cache_save
Run actions/cache/save@v4
"C:\Program Files\Git\usr\bin\tar.exe" --posix -cf cache.tzst --exclude cache.tzst -P -C D:/a/imap-next/imap-next --files-from manifest.txt --force-local --use-compress-program "zstd -T0"
Failed to save: Unable to reserve cache with key Windows|test|1, another job may be creating this cache. More details: Cache already exists. Scope: refs/pull/213/merge, Key: Windows|test|1, Version: e83056fabc1136a6df0cebe07959d02e6e5208f662fe3ab3efa0dd5ffb5bbe27
Warning: Cache save failed.