Merge branch 'fix-checkbox-alignment' into 'master'

Fix inconsistent checkbox alignment

## What does this MR do?
Vertically aligns the checkboxes to the top so that it is aligned with the issue titles

## Are there points in the code the reviewer needs to double check?
None

## Why was this MR needed?
Fixes existing UI inconsistency

## What are the relevant issue numbers?
Closes #21398

## Screenshots (if relevant)
Before:
![Screen_Shot_2016-08-25_at_12.43.21_PM](/uploads/c494d6200e2068feb324db932851cdc0/Screen_Shot_2016-08-25_at_12.43.21_PM.png)

After:
![Screen_Shot_2016-08-25_at_12.41.51_PM](/uploads/42241a150c886592ff92a5840090c589/Screen_Shot_2016-08-25_at_12.41.51_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 !6032

CHANGELOG

@@ -63,6 +63,7 @@ v 8.12.0 (unreleased)
   - Added 'only_allow_merge_if_build_succeeds' project setting in the API. !5930 (Duck)
   - Reduce number of database queries on builds tab
   - Capitalize mentioned issue timeline notes (ClemMakesApps)
+  - Fix inconsistent checkbox alignment (ClemMakesApps)
   - Use the default branch for displaying the project icon instead of master !5792 (Hannes Rosenögger)
   - Adds response mime type to transaction metric action when it's not HTML
   - Fix hover leading space bug in pipeline graph !5980

app/assets/stylesheets/pages/issues.scss

@@ -12,6 +12,10 @@
       padding-right: 8px;
       margin-bottom: 10px;
       min-width: 15px;
+
+      .selected_issue {
+        vertical-align: text-top;
+      }
     }
 
     .issue-labels {