Fixed #24420 -- Allowed ordering by case expressions

django/db/models/expressions.py

@@ -630,6 +630,11 @@ class Ref(ExpressionNode):
     def set_source_expressions(self, exprs):
         self.source, = exprs
 
+    def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
+        # The sub-expression `source` has already been resolved, as this is
+        # just a reference to the name of `source`.
+        return self
+
     def relabeled_clone(self, relabels):
         return self