Make CI badge hitboxes better match container

## What does this MR do?

Makes the Pipeline graph badge hitboxes accurately match their containers.
Currently, there's an issue where the badge highlights, as though, it's clickable, but clicking it does nothing:

![before](/uploads/668f841c640bc586044c89bed9f1e1e9/before.gif)

This is due to the `<a>` and `<button>` elements being padded into the parent elements. So, the parent would react to a cursor, but the cursor wouldn't be on the `<a>`/`<button>` yet.

![before-hitbox](/uploads/6ebaaa4be1096fbfc37f8d73da492c7b/before-hitbox.png)

## Are there points in the code the reviewer needs to double check?

Maybe the tests? I kept the style changes as minimal as possible.

## Why was this MR needed?

I was annoyed every time I clicked on a badge that I was _clearly on_ (it highlighted), but nothing happened.
If I found it irritating, perhaps someone else did too.

## Screenshots (if relevant)

How it behaves in the PR:
![finished](/uploads/c26fabe37ccf17f171f40b48522702b2/finished.gif)

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- Tests
  - [x] All builds are passing
- [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)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #25547 

See merge request !8156