Un-quarantine OAuth spec

What does this MR do?

Un-quarantine OAuth spec

Closes https://gitlab.com/gitlab-org/quality/nightly/issues/100

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