Fix typo

Author: Cito

graphql/subscription/subscribe.py

@@ -36,7 +36,7 @@ async def subscribe(
     compliant subscription, a GraphQL Response (ExecutionResult) with
     descriptive errors and no data will be returned.
 
-    If the the source stream could not be created due to faulty subscription
+    If the source stream could not be created due to faulty subscription
     resolver logic or underlying systems, the coroutine object will yield a
     single ExecutionResult containing `errors` and no `data`.