[import_from_git] Fix crash on first execution with version and cache_path options

[revolter]

Checklist

• [x] I've run bundle exec rspec from the root directory to see all new and existing tests pass
• [x] I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• [x] I see several green ci/circleci builds in the "All checks have passed" section of my PR (connect CircleCI to GitHub if not)
• [x] I've read the Contribution Guidelines
• [x] I've updated the documentation if necessary.
• [x] I've added or updated relevant unit tests.

Motivation and Context

Resolves #21079.

Introduced via #20895 in https://github.com/fastlane/fastlane/releases/tag/2.212.0.

Description

I first decouple import_from_git tests from each other, so I can easier test the fix.

Then, since the initial clone is executed without a checkout, I added a new check to ensure that a checkout gets executed at least once before trying to import the Fastfile.

Testing Steps