Log out after the group template test

What does this MR do?

All QA tests expect to be able to log in at the start of the test.

That's not possible if a test leaves the browser logged in when it finishes. Normally this isn't a problem because Capybara resets the session after each test. But it does that in an after block, so when a test logs in in an after(:all) block, the browser returns to a logged in state after Capybara has logged it out. And then the next test will fail.

E.g.: #34736 (closed)

The fix is to log out once we're done in the after(:all) block.

There's another MR to prevent this from happening in the future: !18978 (merged)

This also updates the test to use Resource::Repository::Commit to commit multiple files in one API call instead of Resource::File, which required four API calls (because there are four files).

Closes #34736 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content