test: assertion equality fix

In test-net-write-callback.js, when process exits, we check callback
count against the expected value. The assertion is written with the
expected value first and actual value second, but that is the opposite
of the documented argument order. Reverse them to be consistent with
documentation.

PR-URL: https://github.com/nodejs/node/pull/24422


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Ouyang Yadong <oyydoibh@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>