Add missing TimeoutException to WaitAsync(TimeSpan, TimeProvider, CancellationToken) documentation (#11481)

Author: Copilot

xml/System.Threading.Tasks/Task.xml

@@ -6382,6 +6382,7 @@ An exception was thrown during
         <returns>The <see cref="T:System.Threading.Tasks.Task" /> representing the asynchronous wait.  It may or may not be the same instance as the current instance.</returns>
         <remarks>To be added.</remarks>
         <exception cref="T:System.ArgumentNullException">The <paramref name="timeProvider" /> argument is <see langword="null" />.</exception>
+        <exception cref="T:System.TimeoutException">The timeout expired. This exception is stored into the returned task.</exception>
         <exception cref="T:System.OperationCanceledException">The cancellation token was canceled. This exception is stored into the returned task.</exception>
       </Docs>
     </Member>