test: fix common.enoughTestMem

A typo introduced in 1ddcb6d2 causes common.enoughTestMem to always
be false, resulting in a lot of tests being skipped. Fix the typo.

PR-URL: https://github.com/nodejs/node/pull/31035


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: David Carlier <devnexen@gmail.com>