Fix undo dismiss should clear comments

What does this MR do and why?

When a finding is reverted back to detected, the dismissal_feedback property should be nullified.

Screenshots or screen recordings

How to set up and validate locally

1. You'll need an EE License
2. You'll need to have runners enabled (See $2408961 for setting up a runner)
3. Enable :refactor_security_extension to turn this feature on.

echo "Feature.enable(:refactor_security_extension)" | rails c

Steps:

1. Import https://gitlab.com/gitlab-examples/security/security-reports
2. Create a new MR by modifying a file
3. Expand the Security Reports Widget from the UI
4. Dismiss a finding
5. Check that there is a Dismissed comment
6. Click again on the same finding to Undo Dismiss
7. Re-open the modal
8. The Dismissed comment should not be visible anymore

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.

Related to #390207 (closed)