Add option to overwrite files on cache extraction

[siburny]

When using GNU tar, if a file already exists, from a previous run or another cached action, it results in a slew of warning messages.

This change adds the use of --overwrite when using GNU tar so that any existing file will just be overwritten.

Similar issue was fixed in the @actions/tool-cache package, but not in @actions/cache: https://github.com/actions/toolkit/pull/807/files#diff-725a5ef102ee3762738a5500c3d7c5b6afef874a1cb67c55085ad5e4615b1a6f