JOINDIN-742: Changing the name and then editing a talk as speaker will remove the speaker-approvement

[ghost]

Jira issue originally created by user heiglandreas:

When a user edits the username and then edits a talk they are approved on as speaker the approval will be lost as the "old" name (approved) will be removed from the talk and the "new" name will be added.

That happens due to TalkMapper::updateSpeakersOnTalk() that only checks the name set in the talk_speaker-table, even though the name displayed in the edit-form is fetched from the user-table.

[github-actions]

This issue has been hanging around a bit too long, if needed please update or comment.