Use `to_reference` where possible.

spec/services/git_push_service_spec.rb

@@ -155,7 +155,7 @@ describe GitPushService do
 
     before do
       allow(commit).to receive_messages(
-        safe_message: "this commit \n mentions ##{issue.iid}",
+        safe_message: "this commit \n mentions #{issue.to_reference}",
         references: [issue],
         author_name: commit_author.name,
         author_email: commit_author.email
@@ -272,4 +272,4 @@ describe GitPushService do
       service.execute(project, user, @blankrev, @newrev, new_ref)
     end
   end
-end
+end
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