CI: Run all RuboCop when config/feature_categories.yml changes

What does this MR do and why?

This MR adds config/feature_categories.yml to RuboCop CI patterns so the job rubocop does a full scan when this file changes.

Previously, rubocop job only tried to check this very file which is a no-op. See https://gitlab.com/gitlab-org/gitlab/-/jobs/3697159937.

Refs #381882 (comment 1261327209) and #381882 (comment 1261621289).

Screenshots or screen recordings

Before	After

How to set up and validate locally remotely

See !110761 (closed) to test a single change of config/feature_categories.yml.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.