child_process: do not ignore proto values of env

This reverts this behaviour introduced in a recent PR, and updates
the test. Without this change, CitGM and other packages are broken.

PR-URL: #18210
Fixes: nodejs/citgm#536
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

lib/child_process.js

@@ -504,7 +504,8 @@ function normalizeSpawnArguments(file, args, options) {
   var env = options.env || process.env;
   var envPairs = [];
 
-  for (const key of Object.keys(env)) {
+  // Prototype values are intentionally included.
+  for (var key in env) {
     const value = env[key];
     if (value !== undefined) {
       envPairs.push(`${key}=${value}`);

test/parallel/test-child-process-env.js

@@ -57,7 +57,7 @@ child.stdout.on('data', function(chunk) {
 
 process.on('exit', function() {
   assert.ok(response.includes('HELLO=WORLD'));
-  assert.ok(!response.includes('FOO='));
+  assert.ok(response.includes('FOO=BAR'));
   assert.ok(!response.includes('UNDEFINED=undefined'));
   assert.ok(response.includes('NULL=null'));
   assert.ok(response.includes(`EMPTY=${os.EOL}`));