Fixes commit message not updating with approved by user

What does this MR do and why?

Fixes a bug where the commit message of a merge request would not update after a user approves it.

Screenshots or screen recordings

1. Update the merge commit message template under project -> merge request settings to include %{approved_by}
2. Open a merge request
3. Click edit commit message in the merge widget
4. Approve the merge request
5. The approved_by text should be updated with the approver users data

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

#432835 (closed)