test: check session timeout in http2

Two instances of a similar test exist, with both testing the timeout on
the stream and neither on the session. Adjust one of them to test the
session timeout instead.

PR-URL: https://github.com/nodejs/node/pull/16754


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>