Example: https://gerrit.wikimedia.org/r/c/mediawiki/core/+/1147132
In integration/config.git:/zuul/layout.yaml, under the extension-quibble template, the test-1.39 pipeline runs the mwgate-node20 job. However, while that template is used by MW extensions, it is not used by mediawiki/core.
mediawiki/core does use the extension-gate template, which runs mwgate-node20 for the "test" and "gate-and-submit" pipelines (master branch) and idem for wmf branches, but not release branches.
mediawiki/core directly also specifies various jobs, but not mwgate-node20 indeed. I'm guessing this got lost in a refactor at some point?