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>