Merge branch '36061-mr-ref-instrument' into 'master'

Instrument MergeRequest#fetch_ref

See merge request !13980

changelogs/unreleased/36061-mr-ref-instrument.yml

+---
+title: Instrument MergeRequest#fetch_ref
+merge_request:
+author:
+type: other

config/initializers/8_metrics.rb

@@ -122,6 +122,7 @@ def instrument_classes(instrumentation)
 
   # Needed for https://gitlab.com/gitlab-org/gitlab-ce/issues/36061
   instrumentation.instrument_instance_method(MergeRequest, :ensure_ref_fetched)
+  instrumentation.instrument_instance_method(MergeRequest, :fetch_ref)
 end
 # rubocop:enable Metrics/AbcSize