test: enable mustCall() during child exit

PR-URL: #16915
Reviewed-By: Khaidi Chu <[email protected]>
Reviewed-By: Gireesh Punathil <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Anatoli Papirovski <[email protected]>
Reviewed-By: Franziska Hinkelmann <[email protected]>

Author: vipinmenon

test/parallel/test-process-raw-debug.js

@@ -50,10 +50,10 @@ function parent() {
     console.log('ok - got expected message');
   });
 
-  child.on('exit', function(c) {
+  child.on('exit', common.mustCall(function(c) {
     assert(!c);
     console.log('ok - child exited nicely');
-  });
+  }));
 }
 
 function child() {