Fix YAML syntax highlight + remove trailing whitespace
minor #3499 Fix YAML syntax highlight + remove trailing whitespace (ifdattic)

This PR was merged into the 2.4 branch.

Discussion
----------

Fix YAML syntax highlight + remove trailing whitespace

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.4
| Fixed tickets |

Commits
-------

0723078 Fix YAML syntax highlight + remove trailing whitespace