test: require handler to be run in sigwinch test

Use `common.mustCall()` to guarantee that the wrapped `_refreshSize()`
functions are invoked.

PR-URL: https://github.com/nodejs/node/pull/11068


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michal Zasso <targos@protonmail.com>