add missing code block directive
minor #3675 add missing code block directive (xabbuh)

This PR was merged into the 2.4 branch.

Discussion
----------

add missing code block directive

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

Thought we already had a pull request for this but didn't find one.

Commits
-------

3ace4d6 add missing code block directive