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>

test/pseudo-tty/test-stderr-stdout-handle-sigwinch.js

@@ -5,7 +5,7 @@ const originalRefreshSizeStderr = process.stderr._refreshSize;
 const originalRefreshSizeStdout = process.stdout._refreshSize;
 
 const wrap = (fn, ioStream, string) => {
-  return () => {
+  const wrapped = common.mustCall(() => {
     // The console.log() call prints a string that is in the .out file. In other
     // words, the console.log() is part of the test, not extraneous debugging.
     console.log(string);
@@ -16,7 +16,8 @@ const wrap = (fn, ioStream, string) => {
       if (!common.isSunOS || e.code !== 'EINVAL')
         throw e;
     }
-  };
+  });
+  return wrapped;
 };
 
 process.stderr._refreshSize = wrap(originalRefreshSizeStderr,