fix type

Author: matthewgrossman

instrumentation/opentelemetry-instrumentation-flask/src/opentelemetry/instrumentation/flask/__init__.py

@@ -275,7 +275,7 @@ def response_hook(span: Span, status: str, response_headers: List):
     def _request_ctx_ref() -> weakref.ReferenceType:
         return weakref.ref(flask.globals.request_ctx._get_current_object())
 else:
-    def _request_ctx_ref() -> int:
+    def _request_ctx_ref() -> weakref.ReferenceType:
         return weakref.ref(flask._request_ctx_stack.top)
 
 def get_default_span_name():