Updating a protected branch overwrites code_owner_approval_required

Summary

Calling PATCH /projects/:id/protected_branches/:name resets the code_owner_approval_required setting of the edited protected branch to false.

Steps to reproduce

1. Enable the Code Owner Approval setting for your branch:

2. Call PATCH /projects/:id/protected_branches/:name like:

curl --request PATCH "https://gitlab.self.managed/api/v4/projects/55843/protected_branches/main" 
-H 'PRIVATE-TOKEN: <GITLAB_TOKEN>' 
-H 'Content-Type: application/json' 
--data '{"allowed_to_merge":[{"access_level":0}]}'

3. Check the Code Owner Approval setting:

Example Project

Not possible as it was reproduced on internally hosted Gitlab and it needs premium to call those endpoints. Which I don't have on gitlab.com.

What is the current bug behavior?

Even though I only wish to set the allowed_to_merge access_level to 0 it also sets the code_owner_approval_required to false.

What is the expected correct behavior?

Because I am not mentioning code_owner_approval_required in the body of the PATCH I am expecting it not to change values.

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Reproduced on version 16.1.3-ee.

Expand for output related to GitLab environment info

(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`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(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)

Possible fixes