Fix branch title trailing space on hover

## What does this MR do?
Removes the unnecessary encapsulation of the `<span>` inside of the `<a>` which was creating the trailing space on hover. 

## Are there points in the code the reviewer needs to double check?
Shouldn't be

## Why was this MR needed?
Makes the UI look more polished

## What are the relevant issue numbers?
Closes #20676 

## Screenshots (if relevant)
Before (When hovering on branch title):
![Screen_Shot_2016-08-05_at_2.54.43_PM](/uploads/1c90ae1ed69268a2fdcdafdede267028/Screen_Shot_2016-08-05_at_2.54.43_PM.png)

After (When hovering on branch title):
![Screen_Shot_2016-08-05_at_2.54.19_PM](/uploads/6eab261a343e7acb6223ed205443b644/Screen_Shot_2016-08-05_at_2.54.19_PM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry 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 you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5688