Tiny optimization (#25175)

* Tiny optimization
- Don't capture the execution context when using UnsafeOnCompleted

Author: davidfowl

src/SignalR/common/Http.Connections/src/Internal/TaskExtensions.cs

@@ -21,6 +21,6 @@ public static async Task NoThrow(this Task task)
         // Observe exception
         public void GetResult() { _ = _task.Exception; }
         public void OnCompleted(Action continuation) => _task.GetAwaiter().OnCompleted(continuation);
-        public void UnsafeOnCompleted(Action continuation) => OnCompleted(continuation);
+        public void UnsafeOnCompleted(Action continuation) => _task.GetAwaiter().UnsafeOnCompleted(continuation);
     }
 }