Fix zstd failing on windows when used with the gnu tar workaround

[lvpx]

This PR aims to resolve the issues #888 and #891 in actions/cache.

Context

We had introduced zstd aliases in actions/cache v3.0.6 to fix issues with zstd failing for tar version < 1.30. That change was made in understanding that we have zstd disabled on windows(bsd tar). However, due to dismal gzip performance on windows runners, developers have been using a workaround to use gnu tar along with zstd. The above release broke this workaround.

Approach

We have switched to using short flag versions(ex. zstd -d) of zstd command for windows on gnu tar instead of the alias versions(ex. unzstd). This restores the workaround functionality same as before the release v3.0.6. This approach has been implemented in this PR.

The downsides of using this approach:

• The change is quite specific in nature and doesn't cover other potential issues we might face with using zstd aliases.

Alternative Approach

We also considered reverting the change done in v3.0.6 and instead implement zstd aliases based on tar versions. This would also work correctly as it has been working before. We only use zstd aliases for tar version < 1.30.

The downside of using this approach:

• Extra system call to tar version to fetch version for every cache call.
• Parsing of tar version stdout output. The tar version is not in semantic versioning format so could be brittle to parse and test.
• Also tar version parsing needs to be implemented.

Feedback is welcome for choosing between both approaches and code review as well. 👀