Fix "Copy to clipboard" action button has a mismatching white background.

## What does this MR do?
Adds a class to all the clipboard icons which removes the extra padding.
It also fixes some odd overlay when over the clipboard icon in commits list.

## Are there points in the code the reviewer needs to double check?
No.

## Why was this MR needed?
To fix the extra padding and background color that was visible when it should not be

## Screenshots (if relevant)
![commits_list](/uploads/f988e2e2e2aea41fe3f7fe41c8a857ef/commits_list.png)
![file](/uploads/ce97909fc4e602af47fea46b8fffb7ad/file.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #22635

See merge request !6785