Create noop pipeline template compatible with test-on-omnibus

andreyrequested to merge
andrey-fix-omnibus-noop into master

What does this MR do and why?

This fixes an issue when omnibus tests trigger would fail in case of a no-op pipeline. This affects backport merge requests with spec only changes like so: https://gitlab.com/gitlab-org/gitlab/-/pipelines/1991749553

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