Enable SpaceAfterVariableColon in scss-lint

What does this MR do?

Enables SpaceAfterVariableColon 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
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

#23485 (moved)

Mentioned in issue #23485 (moved)

Enabled an automatic merge when the build for f035cd48 succeeds

Canceled the automatic merge

Status changed to merged

Mentioned in commit add3a2c4

mentioned in issue gitlab#6675