Resolve "notifications broken during email address change before email confirmed"

What does this MR do?

This fixes an issue where the notification email address would be set to an unconfirmed email address.

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

This logic were not tested at all before this MR, so there are chances that these changes break something...

Why was this MR needed?

Because the notification email address would be set to a unconfirmed email address, which is a potential security (spam) issue.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #22846 (closed)