config: replace confusing use of parse_known_and_unknown_args in _preparse

The way our parser works, "unknown args" or only unknown *flags*. But
`determine_setup` is not interested in those.

Author: bluetech

src/_pytest/config/__init__.py

@@ -1253,7 +1253,7 @@ def _consider_importhook(self, args: Sequence[str]) -> None:
         and find all the installed plugins to mark them for rewriting
         by the importhook.
         """
-        ns, _unknown_args = self._parser.parse_known_and_unknown_args(args)
+        ns = self._parser.parse_known_args(args)
         mode = getattr(ns, "assertmode", "plain")
 
         disable_autoload = getattr(ns, "disable_plugin_autoload", False) or bool(
@@ -1371,13 +1371,11 @@ def _preparse(self, args: list[str], addopts: bool = True) -> None:
                     + args
                 )
 
-        ns, unknown_args = self._parser.parse_known_and_unknown_args(
-            args, namespace=copy.copy(self.option)
-        )
+        ns = self._parser.parse_known_args(args, namespace=copy.copy(self.option))
         rootpath, inipath, inicfg, ignored_config_files = determine_setup(
             inifile=ns.inifilename,
             override_ini=ns.override_ini,
-            args=ns.file_or_dir + unknown_args,
+            args=ns.file_or_dir,
             rootdir_cmd_arg=ns.rootdir or None,
             invocation_dir=self.invocation_params.dir,
         )

src/_pytest/config/argparsing.py

@@ -149,11 +149,11 @@ def parse_known_and_unknown_args(
         namespace: argparse.Namespace | None = None,
     ) -> tuple[argparse.Namespace, list[str]]:
         """Parse the known arguments at this point, and also return the
-        remaining unknown arguments.
+        remaining unknown flag arguments.
 
         :returns:
             A tuple containing an argparse namespace object for the known
-            arguments, and a list of the unknown arguments.
+            arguments, and a list of unknown flag arguments.
         """
         optparser = self._getparser()
         strargs = [os.fspath(x) for x in args]