Always run frontend_fixture as-if-foss with pipeline:run-all-jest label

What does this MR do and why?

This MR resolves CI YAML config error 'jest as-if-foss 1/2' job needs 'rspec-all frontend_fixture as-if-foss' job which occurs when pipeline:run-all-jest label is added to MRs with no matching frontend-patterns-for-as-if-foss pattern, e.g. backend MRs.

Closes #381363 (closed)

Testing

Tested this MR's pipeline configuration changes in !102791 (closed).

code changes	result
backend change with pipeline:run-all-jest (c85ff266)	✅ jest and jest as-if-foss are created: https://gitlab.com/gitlab-org/gitlab/-/pipelines/684054641#/
Regression: backend + frontend change (74e1f19a)	✅ jest minimal and jest minimal as-if-foss are created: https://gitlab.com/gitlab-org/gitlab/-/pipelines/684067761#/
Regression: backend + frontend change with pipeline:run-all-jest (74e1f19a)	✅ jest and jest as-if-foss are created: https://gitlab.com/gitlab-org/gitlab/-/pipelines/684069459#/

How to set up and validate locally

1. Create a MR with backend changes, e.g. !102791 (closed) by setting 381363-fix-ci-config-yaml as a target branch.
2. Add pipeline:run-all-jest label.
3. Trigger new pipeline, e.g. https://gitlab.com/gitlab-org/gitlab/-/pipelines/684018176#/.

MR acceptance checklist

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