Required Pipeline Configuration resetting to "No Required Pipeline"
### Summary
One of our customers reported the the value of **Required Pipeline Configuration** is being reset to **No Required Pipeline**.
Based on my test, it seems that this is happening when changing other configurations in the **Admin Area**.
### Steps to reproduce
1. Go to **Admin Area** -> **Settings** -> **CI/CD**.
1. Set a value of **Required pipeline configuration**.
1. Click **Save changes**.
1. Change a different configuration in the page, e.g, **Package Registry**.
1. Click **Save changes**.
1. Notice that the value for **Required Pipeline Configuration** has been reset to the default value.
### What is the current *bug* behavior?
**Required Pipeline Configuration** resets its values.
### What is the expected *correct* behavior?
**Required Pipeline Configuration** retains its values whenever we change a setting in **Admin Area**.
### Relevant logs and/or screenshots
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### Possible fixes
This bug might be caused by this MR: [Allow unsetting "Required pipeline configuration" for CI/CD](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/28432)
### Customer information
- https://gitlab.zendesk.com/agent/tickets/173702 (internal)
- https://gitlab.my.salesforce.com/00161000004zrG3AAI (internal)
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