Correct audit message text to mention committers instead of reviewers

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR updates the string that gets created for an audit event when the Prevent approval from committers MR settings checkbox is changed. It previously indicated "reviewers" instead of "committers" in the audit event message.

✅ Question: This MR will update the messages for these events going forward, but what do we do about historical audit events that already exist?

• As discussed in the comment threads below, we will update the docs to indicate the message change but not update previously created events.

Related #339473 (closed)

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

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.