Merge branch 'add-refs' into 'master'

Include merge-requests in RESERVED_REFS_NAMES

See merge request gitlab-org/gitlab!82326

app/models/repository.rb

@@ -15,6 +15,7 @@ class Repository
     heads
     tags
     replace
+    #{REF_MERGE_REQUEST}
     #{REF_ENVIRONMENTS}
     #{REF_KEEP_AROUND}
     #{REF_PIPELINES}