Unable to create pipeline with frontend and feature flag labels in gitlab-org/gitlab project

Summary

CI displays a yaml invalid error when attempting to create a pipeline for an MR that has both the frontend and feature flag labels applied.

See this pipeline for an example:

Steps to reproduce

1. Create a new MR in the https://gitlab.com/gitlab-org/gitlab project after making a change to any file, for example, add a comment to qa/qa/specs/features/ee/browser_ui/13_secure/merge_request_license_widget_spec.rb:

   +++ b/qa/qa/specs/features/ee/browser_ui/13_secure/merge_request_license_widget_spec.rb
   @@ -1,5 +1,6 @@
    # frozen_string_literal: true
   
   +# testing
    module QA
      RSpec.describe 'Secure', :runner, product_group: :composition_analysis, feature_flag: {
        name: 'license_scanning_sbom_scanner'

2. Add both a feature flag and frontend label to the MR, for exmaple:

   /label ~"Category:License Compliance" ~"Deliverable" ~"GitLab Ultimate" ~"QA" ~"backend" ~"devops::secure" ~"feature flag" ~"feature::enhancement" ~"group::composition analysis" ~"section::sec" ~"type::feature" ~frontend 

3. View pipeline for MR and see Unable to create pipeline error.

Example Project

!113478 (closed)

What is the current bug behavior?

Can't create a pipeline for an MR.

What is the expected correct behavior?

Pipeline for a MR should be created successfully.

Possible fixes

There's a problem with the rules in https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/ci/rules.gitlab-ci.yml#L101. According to @rymai in a slack conversation:

we probably need to add - <<: *if-merge-request-labels-frontend-and-feature-flag to .test-metadata:rules:retrieve-tests-metadata.