Unable to toggle "Trigger builds for mirror updates" option

Summary

Toggling Trigger builds for mirror updates appears to do something, but results in nothing.

Steps to reproduce

1. Setup a mirror
2. Navigate to https://gitlab.com/<user>/<repo>/pipelines/settings
3. Try to turn Trigger builds for mirror updates option on (it's off by default)
4. Click Save changes

Expected behavior

Changes are saved, page is reloaded and everything works.

Actual behavior

Save changes button stays greyed out and changes are not saved.

Relevant logs and/or screenshots

I captured the request sent after hitting Save changes button and am posting it in HAR format with PII stripped:

request.har