Exclude secure jobs from docs pipelines

What does this MR do?

The secure jobs should not be running on docs-only branches. I believe when the rules were added, we forgot to add the exception. See https://gitlab.com/gitlab-org/gitlab-runner/-/pipelines/215436230:

The code quality job can be excluded as well, but I'll fix that in a separate MR.

Why was this MR needed?

What's the best way to test this MR?

What are the relevant issue numbers?