cmake: Fix FindLibGit2.cmake with newer versions

[Vogtinator]

Update the REGEX to also allow tabs.

Basics

• [x] Short descriptions of your changes are in the release notes (added as entry in doc/news/_preparation_next_release.md which contains _(my name)_) Please always add something to the release notes.
• [x] Details of what you changed are in commit messages (first line should have module: short statement syntax)
• [x] References to issues, e.g. close #X, are in the commit messages.
• [ ] The buildservers are happy. If not, fix in this order:
  • [ ] add a line in doc/news/_preparation_next_release.md
  • [ ] reformat the code with scripts/dev/reformat-all
  • [ ] make all unit tests pass
  • [ ] fix all memleaks
• [x] The PR is rebased with current master.

Checklist

• [ ] I added unit tests for my code
• [x] I fully described what my PR does in the documentation (not in the PR description)
• [] I fixed all affected documentation
• [ ] I added code comments, logging, and assertions as appropriate (see Coding Guidelines)
• [ ] I updated all meta data (e.g. README.md of plugins and METADATA.ini)
• [ ] I mentioned every code not directly written by me in reuse syntax

Review

• [ ] Documentation is introductory, concise, good to read and describes everything what the PR does
• [ ] Examples are well chosen and understandable
• [ ] Code is conforming to our Coding Guidelines
• [ ] APIs are conforming to our Design Guidelines
• [ ] Code is consistent to our Design Decisions

Labels

• [ ] Add the "work in progress" label if you do not want the PR to be reviewed yet.
• [ ] Add the "ready to merge" label if the basics are fulfilled and no further pushes are planned by you.

[markus2330]

Thank you for the PR! Looks good to me, let us see if it will pass all build server tests.

[markus2330]

jenkins build libelektra please

[markus2330]

Great job! Looking forward to more PRs :heart: