Checksum not constant when using git_config

[Louwrensth]

Using sources with git_config has a limitation that the checksums feature does not work as it is not constant because the timestamp of files are included in the .gz.
Something similar is noted in the docs:

Note Because the source tarball is created locally (by running tar cfvz on the directory containing the cloned repository), the (SHA256) checksum is not guaranteed to be the same across different systems.

I propose a small change that can help here: use gzip --no-name to compress instead of using tar cfvz.

Another option is to use bzip2, i.e. tar cfvj.

[boegel]

See also PR #2727