Update `Git::Repository` to handle changes made while a test was disabled

What does this MR do?

Fixes the git protocol v2 tests.

The tests haven't been running for a while, so when run output was changed from a string to a struct, QA::Git::Repository#fetch_supported_git_protocol wasn't updated to handle run output properly because nothing was using the method at the time.

The SSH test still fails because of gitlab-shell#273 (closed)

That should not prevent this MR from being merged because the tests are still in quarantine and will stay there until gitlab-shell#273 (closed) is addressed and the rest of the plan in https://gitlab.com/gitlab-org/quality/team-tasks/issues/388 is followed to verify the tests pass before removing them from quarantine.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done