Fix file locking spec and quarantine locks directory spec

What does this MR do?

1. Quarantine /qa/specs/features/ee/browser_ui/3_create/repository/file_locking_spec.rb:33('locks a directory and tries to push as a second user') - due to an actual bug #35254 (closed)
2. Update hardcoded Administrator expectation to username

Issue: #35153 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content