Do not warn changelog required when removing feature flag patches

`Danger` checks if we are removing feature flag files without a
changelog entry and reports:

This merge request requires a changelog entry because it
[removes a feature flag](https://docs.gitlab.com/ee/development/changelog.html#what-warrants-a-changelog-entry).

[This happens inside the gitlab-dangerfiles](https://gitlab.com/gitlab-org/ruby/gems/gitlab-dangerfiles/-/blob/master/lib/danger/plugins/changelog.rb?ref_type=heads#L38)

As far as I can tell we only use the feature flag category in danger for
this specific check so we don't need to recategorize the patch files.

Fixes https://gitlab.com/gitlab-org/gitlab/-/issues/506518

Changelog: fixed

spec/tooling/danger/project_helper_spec.rb

@@ -35,6 +35,19 @@
       'doc/api/openapi/openapi.yaml'                     | [:docs, :backend]
       'doc/api/openapi/any_other_file.yaml'              | [:docs, :backend]
 
+      'config/feature_flags/flag_config.yml' | [:feature_flag]
+      'config/feature_flags/nested/flag_config.yaml' | [:feature_flag]
+      'ee/config/feature_flags/flag_config.yml' | [:feature_flag]
+      'ee/config/feature_flags/nested/flag_config.yaml' | [:feature_flag]
+      'jh/config/feature_flags/flag_config.yml' | [:feature_flag]
+      'jh/config/feature_flags/nested/flag_config.yaml' | [:feature_flag]
+      'config/feature_flags/flag_config.patch' | [:backend]
+      'config/feature_flags/nested/flag_config.patch' | [:backend]
+      'ee/config/feature_flags/flag_config.patch' | [:backend]
+      'ee/config/feature_flags/nested/flag_config.patch' | [:backend]
+      'jh/config/feature_flags/flag_config.patch' | [:backend]
+      'jh/config/feature_flags/nested/flag_config.patch' | [:backend]
+
       'usage_data.rb'   | [:database, :backend, :analytics_instrumentation]
       'doc/foo.md'      | [:docs]
       'CONTRIBUTING.md' | [:docs]

tooling/danger/project_helper.rb

@@ -23,7 +23,7 @@ module ProjectHelper
 
         [%r{usage_data\.rb}, %r{^(\+|-).*\s+(count|distinct_count|estimate_batch_distinct_count)\(.*\)(.*)$}] => [:database, :backend, :analytics_instrumentation],
 
-        %r{\A((ee|jh)/)?config/feature_flags/} => :feature_flag,
+        %r{\A((ee|jh)/)?config/feature_flags/.*(\.(yml|yaml))\z} => :feature_flag,
 
         %r{doc/api/usage_data.md} => [:analytics_instrumentation],