Migrate protected branch form errors

What does this MR do and why?

Migrate errors form for protected branch project repository settings

Closes #364880 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Open a project where you have admin rights
2. Navigate to Settings -> Repository http://localhost:3000/flightjs/Flight/-/settings/repository
3. Expand protected branches section
4. Trigger an error, for example by adding this line to the haml - @protected_branch.errors.add(:base, "Something went wrong")
5. Observe change form error

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.