test: add check for root user

Currently this test fails if run as the root user:
Mismatched innerFn function calls. Expected exactly 62, actual 42.

The motivation for this is that when building node in a docker
container it is convenient to be able to build as root.

test/parallel/test-child-process-spawnsync-validation-errors.js

@@ -3,11 +3,12 @@ const common = require('../common');
 const assert = require('assert');
 const spawnSync = require('child_process').spawnSync;
 const signals = process.binding('constants').os.signals;
+const rootUser = process.getuid() === 0;
 
 let invalidArgTypeError;
 let invalidArgTypeErrorCount = 62;
 
-if (common.isWindows) {
+if (common.isWindows || rootUser) {
   invalidArgTypeError =
     common.expectsError({ code: 'ERR_INVALID_ARG_TYPE', type: TypeError }, 42);
 } else {
@@ -64,7 +65,7 @@ function fail(option, value, message) {
 if (!common.isWindows) {
   {
     // Validate the uid option
-    if (process.getuid() !== 0) {
+    if (!rootUser) {
       pass('uid', undefined);
       pass('uid', null);
       pass('uid', process.getuid());