Allow git-lfs-transfer integration tests to be skipped

[fh1ch]

This PR introduces the new environment variable TEST_SKIP_LFS_TRANSFER which offers the possibility to skip git-lfs-transfer tests based on scutiger-lfs while also running within CI:

make integration TEST_SKIP_LFS_TRANSFER=true

This is required since it's currently not possible to disable the use of git-lfs-transfer when running within a CI build (detected automatically via CI variable). Since git-lfs-transfer has to be installed on a systems via other means, most external CI builds will fail as they can't use the git-lfs Docker test image, which preinstalls git-lfs-transfer.

This is patch needed to make git-lfs packaging work for Linux distributions like Alpine Linux (e.g. see https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/26213).

An alternative to the approach used within this PR would be to change the logic to a positive one, meaning replacing the current $CI && !$TEST_SKIP_LFS_TRANSFER with an e.g. $USE_GIT_LFS_TRANSFER one. This would disable those tests on all environments, allowing the git-lfs CI test to explicitly enable them.

/cc @bk2204

[bk2204]

Hey,

My preference here is that we do either one of two things:

• Not set CI in environments other than the Git LFS CI, which I think makes things more robust.
• Name the new environment variable starting with TEST (e.g., TEST_SKIP_LFS_TRANSFER), which is what our other tests do.

[fh1ch]

@bk2204 thanks a lot for the feedback. Not setting CI is not really feasible IMO, as this is automatically done by pretty much every CI system like GitHub Action, GitLab CI, Jenkins, ... It would require the creation a completely empty env via other means.

I really like the TEST_SKIP_LFS_TRANSFER name change tough, especially since there already seems to be an established practise. I just reworked the MR to that, let me know what you think.

[bk2204]

Looks good. Once CI is green, I'll merge this.