Set status check back to pending on retry

What does this MR do and why?

What

Sets a status check status back to pending when retry is hit

Why

Allows users to see that a retry is occurring and is pending instead of failed

Screenshots or screen recordings

Old	New

How to set up and validate locally

1. Simulate a SaaS instance (export GITLAB_SIMULATE_SAAS=1)

2. Under Project > Settings > Merge Requests > Status Checks

   Add some example status checks (see example screenshot below):

   

3. Create an MR (Edit the README.md of any project using the WebIDE and create an MR)

4. Set a status check's status to failure using the API: POST gdk.test:3000/api/v4/projects/<project_id>/merge_requests/<merge_request_id>/status_check_responses with a JSON body of:

   {
   "sha": <sha_of_latest_merge_to_branch>,
   "external_status_check_id": "1",
   "status": "failed"
   }

5. Press retry

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 #388894 (closed)