Fix no-external

yt_dlp/__init__.py

@@ -433,6 +433,8 @@ def validate_options(opts):
     opts.plugin_dirs = opts.plugin_dirs or []
     if 'no-external' not in opts.plugin_dirs:
         opts.plugin_dirs.append('external')
+    else:
+        opts.plugin_dirs.remove('no-external')
 
     if opts.playlist_items is not None:
         try:

yt_dlp/plugins.py

@@ -169,7 +169,7 @@ class PluginFinder(importlib.abc.MetaPathFinder):
 
 def directories():
     spec = importlib.util.find_spec(PACKAGE_NAME)
-    return spec.submodule_search_locations if spec else []
+    return list(spec.submodule_search_locations) if spec else []
 
 
 def iter_modules(subpackage):