[ci] No cache hits on Bazel Windows cache.

[agutkin]

We don't get any cache hits on the Bazel cache on Windows. Fix.

[agutkin]

This may need to be reopened: The cache is now hit correctly, but the cache posting by tar.exe fails:

Post job cleanup.
C:\Windows\System32\tar.exe --posix -z -cf cache.tgz -P -C D:/a/mozolm/mozolm --files-from manifest.txt
tar.exe: Couldn't open C:/Users/runneradmin/_bazel_runneradmin/jcqm7o2t/java.log.fv-az171-286.runneradmin.log.java.20210512-222522.1120: Permission denied
tar.exe: Error exit delayed from previous errors.
Warning: Tar failed with error: The process 'C:\Windows\System32\tar.exe' failed with exit code 1

See actions/toolkit#632.

[agutkin]

The presubmit run for #101 looks better now:

Post job cleanup.
C:\msys64\usr\bin\tar.exe --posix --use-compress-program "zstd -T0" -cf cache.tzst -P -C D:/a/mozolm/mozolm --files-from manifest.txt --force-local
Cache Size: ~1197 MB (1255091279 B)
Cache saved successfully
Cache saved with key: Windows-bazel-f4cbf5a91f93d09549716b4533757e19cdfe152eabb430876f4a33d3b3d5f584

[agutkin]

Cache is now generated and hit upon the next build. However it looks like when it's restored, tar cannot create symbolic links. Keeping this issue open for further investigation.