Fix python3-ism in test_other.py (emscripten-core#9915)

See: emscripten-core#9875

Author: sbc100

tests/test_other.py

@@ -9036,7 +9036,8 @@ def test_node_js_pthread_module(self):
   process.exit(0);
 });
 '''
-    os.makedirs('subdir', exist_ok=True)
+    if not os.path.exists('subdir'):
+      os.mkdir('subdir')
     create_test_file(os.path.join('subdir', moduleLoader), moduleLoaderContents)
 
     # build hello_world.c