Disable Metrics/AbcSize cop on metrics initializer

On a previous commit it was enabled but after the CE Upstream merge it
needed to be disabled again

config/initializers/8_metrics.rb

@@ -3,6 +3,7 @@
 # that we can stub it for testing, as it is only called when metrics are
 # enabled.
 #
+# rubocop:disable Metrics/AbcSize
 def instrument_classes(instrumentation)
   instrumentation.instrument_instance_methods(Gitlab::Shell)
 
@@ -117,6 +118,7 @@ def instrument_classes(instrumentation)
   # Needed for https://gitlab.com/gitlab-org/gitlab-ce/issues/30224#note_32306159
   instrumentation.instrument_instance_method(MergeRequestDiff, :load_commits)
 end
+# rubocop:enable Metrics/AbcSize
 
 # With prometheus enabled by default this breaks all specs
 # that stubs methods using `any_instance_of` for the models reloaded here.