Ensure users can unlink Group SAML when the group has SAML disabled

What

Ensures that users can unlink / distrust SAML for a group that has had its Group SAML trial expire.

Closes #217817 (closed)

Why

If users no longer trust a group to sign them into GitLab they must be able to unlink the authentication method.

Screenshots

Acceptance criteria

Conformity

• Changelog entry
• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.