Security scan widget not loading in merge requests – security reports keep returning 204 status
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### Summary
For an MR with successful pipeline (security jobs are finished successfully), the security scan widget keeps loading. Requests being made to `security_reports` keep returning status 204, even after many minutes.
<!-- Summarize the bug encountered concisely. -->
### Steps to reproduce
<!-- Describe how one can reproduce the issue - this is very important. Please use an ordered list. -->
### Example Project
_Adding in confidential note below._
### What is the current *bug* behavior?
1. Go to merge request
2. Notice that latest pipeline has finished
3. Notice the security widget keeps loading. Requests to `gitlab.com/\<project_path\>/\<mr_iid\>/security_reports` keep returning status code 204.
### What is the expected *correct* behavior?
1. Go to merge request
2. Security widget should load but not indefinitely. Requests to `security_reports` should return results with status code 200 after a while.
### Relevant logs and/or screenshots
_Adding in confidential note below._
### Output of checks
<!-- If you are reporting a bug on GitLab.com, uncomment below -->
This bug happens on GitLab.com
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<!-- or follow up with an issue comment of `@gitlab-bot label ~"reproduced on GitLab.com"` if you do not -->
#### Results of GitLab environment info
<!-- Input any relevant GitLab environment information if needed. -->
<details>
<summary>Expand for output related to GitLab environment info</summary>
<pre>
(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)
(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)
</pre>
</details>
#### Results of GitLab application Check
<!-- Input any relevant GitLab application check information if needed. -->
<details>
<summary>Expand for output related to the GitLab application check</summary>
<pre>
(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:check SANITIZE=true`)
(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true`)
(we will only investigate if the tests are passing)
</pre>
</details>
### Possible fixes
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### Patch release information for backports
If the bug fix needs to be backported in a [patch release](https://handbook.gitlab.com/handbook/engineering/releases/patch-releases) to a version
under [the maintenance policy](https://docs.gitlab.com/policy/maintenance/), please follow the steps on the
[patch release runbook for GitLab engineers](https://gitlab.com/gitlab-org/release/docs/-/blob/master/general/patch/engineers.md).
Refer to the [internal "Release Information" dashboard](https://dashboards.gitlab.net/d/delivery-release_info/delivery3a-release-information?orgId=1)
for information about the next patch release, including the targeted versions, expected release date, and current status.
#### High-severity bug remediation
To remediate high-severity issues requiring an [internal release](https://handbook.gitlab.com/handbook/engineering/releases/internal-releases/) for single-tenant SaaS instances,
refer to the [internal release process for engineers](https://gitlab.com/gitlab-org/release/docs/-/blob/master/general/internal-releases/engineers.md?ref_type=heads).
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issue