push preserved contexts in correct order

src/flask/testing.py

@@ -240,10 +240,10 @@ class FlaskClient(Client):
         response.json_module = self.application.json  # type: ignore[assignment]
 
         # Re-push contexts that were preserved during the request.
-        while self._new_contexts:
-            cm = self._new_contexts.pop()
+        for cm in self._new_contexts:
             self._context_stack.enter_context(cm)
 
+        self._new_contexts.clear()
         return response
 
     def __enter__(self) -> FlaskClient: