test: fix test-cli-syntax assertions on windows

The test introduced in a5f91ab230
accidentally introduced failures on some windows builds. Update the
assertion that was causing the failures.

PR-URL: https://github.com/nodejs/node/pull/12212
Ref: https://github.com/nodejs/node/pull/11689
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-cli-syntax.js

@@ -124,9 +124,10 @@ syntaxArgs.forEach(function(args) {
     const args = [checkFlag, evalFlag, 'foo'];
     const c = spawnSync(node, args, {encoding: 'utf8'});
 
-    assert.strictEqual(
+    assert(
-      c.stderr,
+      c.stderr.startsWith(
-      `${node}: either --check or --eval can be used, not both\n`
+        `${node}: either --check or --eval can be used, not both`
+      )
     );
 
     assert.strictEqual(c.status, 9, 'code === ' + c.status);