Fix the rules for testing single dockerfiles

What does this MR do and why?

Axil noticed in !3791 (comment 1364219454) that the test:image:docs-single job didn't run in his MR. Turns out we had tagged the wrong rules to that job (and the lunrjs equivalent).

I tested it in the pipeline for this commit (6776e2a8), which updated the pipeline config and touched all the dockerfiles. You can see the two test:image:docs-single and test:image:docs-single-lunrjs jobs in the pipeline.

I then pulled the dockerfile changes, and kept the pipeline fix.

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