test(auth): mark async timeout coverage arc

Author: Jianke LIN

tests/server/auth/test_get_access_token_streamable_http.py

@@ -144,5 +144,5 @@ async def handle_progress(ctx: ServerRequestContext, params: ProgressNotificatio
 
             auth.token = "token-B"
             await client.send_progress_notification("token-B", 0.2)  # pyright: ignore[reportDeprecated]
-            with anyio.fail_after(5):
+            with anyio.fail_after(5):  # pragma: no branch - coverage misreports the normal context exit arc
                 assert await receive_token.receive() == "token-B"