test: deflake http2-cancel-while-client-reading

Add missing `'error'` event handler.

Fixes: https://github.com/nodejs/node/issues/40610

PR-URL: https://github.com/nodejs/node/pull/40659
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-http2-cancel-while-client-reading.js

@@ -20,6 +20,7 @@ server.on('stream', common.mustCall(function(stream) {
     client_stream.pause();
     client_stream.close(http2.constants.NGHTTP2_CANCEL);
   });
+  stream.on('error', () => {});
 }));
 
 server.listen(0, function() {