test: add mustCall to test-net-after-close test

PR-URL: https://github.com/nodejs/node/pull/27459


Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Yorkie Liu <yorkiefixer@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>