LDAP e2e tests: Ensure correct group owner role and Un-quarantine test

What does this MR do?

Reuses group.add_member and provides it with the correct user (with the right user.id) and role to ensure owner role for the user.

FYI - I believe this test was quarantined on the first failing incident. It has been quite stable and the changes in this MR should improve on that.

Conformity

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