Honor --skip-install for extension installers

Author: catboxanon

modules/launch_utils.py

@@ -224,6 +224,9 @@ def run_extension_installer(extension_dir):
     if not os.path.isfile(path_installer):
         return
 
+    if args.skip_install:
+        return
+
     try:
         env = os.environ.copy()
         env['PYTHONPATH'] = f"{os.path.abspath('.')}{os.pathsep}{env.get('PYTHONPATH', '')}"