test: fix flaky test-gc-net-timeout

There's a global.gc() invoked in an interval, and a second one in a
req.setTimeout() callback. Remove the one in the callback. I'm not sure
how competing global.gc() calls might result in a deadlock, but it seems
plausible and empirical testing confirms that it makes the test
reliable.

Fixes: https://github.com/nodejs/node/issues/23067

PR-URL: https://github.com/nodejs/node/pull/23139


Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>