Merge branch 'enable-scss-lint-space-around-operator' into 'master'

Enable SpaceAroundOperator in scss-lint

## What does this MR do?
Enables `SpaceAroundOperator` in .`scss-lint.yml`

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

## Why was this MR needed?
Improve SCSS maintainability and consistency

## Screenshots (if relevant)
None

## Does this MR meet the acceptance criteria?

- Tests
  - [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?
#23485

See merge request !7078

.scss-lint.yml

@@ -201,7 +201,7 @@ linters:
   # Operators should be formatted with a single space on both sides of an
   # infix operator.
   SpaceAroundOperator:
-    enabled: false
+    enabled: true
   
   # Opening braces should be preceded by a single space.
   SpaceBeforeBrace:

app/assets/stylesheets/framework/modal.scss

@@ -3,7 +3,7 @@
   padding: 15px;
 
   .form-actions {
-    margin: -$gl-padding+1;
+    margin: -$gl-padding + 1;
     margin-top: 15px;
   }
 

app/assets/stylesheets/pages/note_form.scss

@@ -8,7 +8,7 @@
 .diff-file .diff-content {
   tr.line_holder:hover > td .line_note_link {
     opacity: 1.0;
-    filter: alpha(opacity=100);
+    filter: alpha(opacity = 100);
   }
 }