pluginupdate.py: support comments

when maintaining out of tree plugins, it makes it easier to swap/comment on specific plugins

maintainers/scripts/pluginupdate.py

@@ -401,6 +401,8 @@ def load_plugin_spec(plugin_file: str) -> List[PluginDesc]:
     plugins = []
     with open(plugin_file) as f:
         for line in f:
+            if line.startswith("#"):
+                continue
             plugin = parse_plugin_line(line)
             if not plugin.owner:
                 msg = f"Invalid repository {line}, must be in the format owner/repo[ as alias]"