Corrective action: www-gitlab-com pipelines failing with "Undefined error"

Summary

A corrective action to update the feature flag check in lib/gitlab/ci/config/external/mapper/verifier.rb was identified in production#8405 (comment 1280469809)

Related Incident(s)

Originating issue(s): production#8405 (closed)

Context

Upon rolling out the FF ci_includes_count_duplicates introduced by Update CI includes counting structure to includ... (gitlab-org/gitlab!111726 - merged), an incident occurred, which was due to mismatching Feature Flag project actors. This is explained in more detail here.

The specific error that arose was due to .add being called on an Array.

Desired Outcome/Acceptance Criteria

Replace the Feature Flag condition with a variable type check. Ref: gitlab-org/gitlab!111726 (diffs)

                if ::Feature.enabled?(:ci_includes_count_duplicates, context.project)
                  context.expandset << file
                else
                  context.expandset.add(file)
                end

Desired outcome: In a situation where a project (with FF enabled) has a .gitlab-ci.yml config that includes a file from another project (with FF disabled), there will be no error when running the pipeline.

Associated Services

Corrective Action Issue Checklist

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