test: set Git name and email.

[MikeMcQuaid]

Extract the code from bottle.rb into utils/git.rb and ensure it's run before we run tests.

Should resolve issues like in Homebrew/homebrew-core#50328

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

---