Resolve "Reply-by-email did not pick up /unsubscribe quick action"

What does this MR do?

Allow users who can't update the noteable to perform the quick actions that don't need that access.

Are there points in the code the reviewer needs to double check?

Don't think so!

Why was this MR needed?

It's a bug, and it caused @toon some issues.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend

What are the relevant issue numbers?

Closes #43334 (closed).