Prevent adding same role multiple times on repeated clicks

What does this MR do?

Fixes a bug where clicking multiple times on role No one while marking a branch or tag protected causes to increases role count with each click made, and since the information is cached in localStorage, this makes it impossible to use the feature without deleted storage data after the bug occurs.

Screenshots

Refer to the video attached in the original issue, and then try to reproduce the same in this branch.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] API support added
• [ ] Tests added for this feature/bug
• Review
  • [ ] Has been reviewed by UX
  • Has been reviewed by Frontend
  • [ ] Has been reviewed by Backend
  • [ ] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• [ ] Internationalization required/considered
• [ ] If paid feature, have we considered GitLab.com plan and 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 #4294 (closed)