Pushing to a merge request clears the approvals list if the respective project setting is enabled

What does this MR do?

When "approvals in a merge request when new commits are pushed to its source branch" project setting is enabled and the "Approvals required" number is 0, the approvals would not be cleared when pushing new commits to a merge request.

This merge request aims to fix that inconsistency

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?

What are the relevant issue numbers?

Closes #6702 (closed)