Extract a do_execute method to be overridden

This way we don't have to duplicate the guard

app/services/merge_requests/refresh_service.rb

@@ -5,6 +5,12 @@ module MergeRequests
     def execute(oldrev, newrev, ref)
       return true unless Gitlab::Git.branch_ref?(ref)
 
+      do_execute(oldrev, newrev, ref)
+    end
+
+    private
+
+    def do_execute(oldrev, newrev, ref)
       @oldrev, @newrev = oldrev, newrev
       @branch_name = Gitlab::Git.ref_name(ref)
 
@@ -30,8 +36,6 @@ module MergeRequests
       true
     end
 
-    private
-
     def close_upon_missing_source_branch_ref
       # MergeRequest#reload_diff ignores not opened MRs. This means it won't
       # create an `empty` diff for `closed` MRs without a source branch, keeping

ee/app/services/ee/merge_requests/refresh_service.rb

@@ -3,15 +3,13 @@ module EE
     module RefreshService
       extend ::Gitlab::Utils::Override
 
-      override :execute
-      def execute(oldrev, newrev, ref)
-        return true unless ::Gitlab::Git.branch_ref?(ref)
+      private
 
+      override :do_execute
+      def do_execute(oldrev, newrev, ref)
         super && reset_approvals_for_merge_requests(ref, newrev)
       end
 
-      private
-
       # Note: Closed merge requests also need approvals reset.
       def reset_approvals_for_merge_requests(ref, newrev)
         branch_name = ::Gitlab::Git.ref_name(ref)