Fixed file template dropdown for the "New File" editor for smaller/zoomed screens

## What does this MR do?

Fixes the dropdown issue on zoomed/smaller screens

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

Until what point do we consider not supporting a certain screen size / zoom level

## Why was this MR needed?

To fix the dropdown position when zooming in on the screen

## Screenshots (if relevant)

Zoom levels

**100% Zoom**
![100_](/uploads/b13c6c48d4ca99b119d45975280cd16f/100_.png)

**175% Zoom**
![175_](/uploads/ef25dffbf85d0859bc57c875914ffc7a/175_.png)

**200% Zoom**
![200_](/uploads/6ff7709f42304d51ef29a173efa5540d/200_.png)

**300% Zoom**
![300_](/uploads/7e57528582a09355354bbbfc26aa64a4/300_.png)

## Does this MR meet the acceptance criteria?

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

## What are the relevant issue numbers?

Closes #23962 

## Affected pages for the modified css-classes

`./app/assets/stylesheets/pages/editor.scss:  .gitignore-selector,
./app/assets/stylesheets/pages/editor.scss:  .license-selector,
./app/assets/stylesheets/pages/editor.scss:  .gitlab-ci-yml-selector {
./app/views/projects/blob/_editor.html.haml:      .gitlab-ci-yml-selector.js-gitlab-ci-yml-selector-wrap.hidden
./app/assets/stylesheets/pages/editor.scss:  .new-file-name {
./app/views/projects/blob/_editor.html.haml:        required: true, class: 'form-control new-file-name' `

See merge request !7807