httpserver_test: Add ExpectLog to fix CI

The github security advisory feature lets you make private PRs but
it apparently doesn't support CI so this log failure wasn't caught
until after the PR was merged.

tornado/test/httpserver_test.py

@@ -575,9 +575,10 @@ def test_chunked_request_body_invalid_size(self):
                 b"\n", b"\r\n"
             )
         )
-        start_line, headers, response = self.io_loop.run_sync(
-            lambda: read_stream_body(self.stream)
-        )
+        with ExpectLog(gen_log, ".*invalid chunk size", level=logging.INFO):
+            start_line, headers, response = self.io_loop.run_sync(
+                lambda: read_stream_body(self.stream)
+            )
         self.assertEqual(400, start_line.code)
 
     @gen_test