Bugfix: Only use git for build info if the repository is actually the right one

[luke-jr]

Fixes using unrelated git repos again, after the fix in #7522 was unexplicably removed by #18556

Also (really) fixes the "build version hack" (#18349) by embedding the correct tag in the release genbuild.sh

Based on top of #18818 to avoid unnecessary conflicts/rebasing once that's merged

[DrahtBot]

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

Conflicts

Reviewers, this pull request conflicts with the following ones:

• gitian: Bump descriptors to Focal for 22.0 #21036 (gitian: Bump descriptors to Focal for 22.0 by fanquake)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

[DrahtBot]

🐙 This pull request conflicts with the target branch and needs rebase.

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[maflcko]

Closing for now. This needs rebase and there hasn't been any activity for months.

You can leave a comment if you want this to be reopened. (Or create a new pull, since there haven't been any comments here). Though, please make sure the code is passing tests and is ready for review.