config: remove an unneeded Namespace copy

Author: bluetech

src/_pytest/config/__init__.py

@@ -1501,9 +1501,7 @@ def parse(self, args: list[str], addopts: bool = True) -> None:
         # are going to be loaded.
         self.pluginmanager.consider_env()
 
-        self.known_args_namespace = self._parser.parse_known_args(
-            args, namespace=copy.copy(self.known_args_namespace)
-        )
+        self._parser.parse_known_args(args, namespace=self.known_args_namespace)
 
         self._validate_plugins()
         self._warn_about_skipped_plugins()