Fix save button on pipelines settings page

## What does this MR do?

This MR fixes 'Save button' on pipeline settings page, which didn't change state to enabled after saving settings.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing

## What are the relevant issue numbers?

Closes #23431

See merge request !6955