Update api.py

Add NETRC to the list of default_pass_env. This is used by pip when downloading package from an index needing authentication.

Author: chipot

src/tox/tox_env/api.py

@@ -220,6 +220,7 @@ def _default_pass_env(self) -> list[str]:  # noqa: PLR6301
             "HOME",  # needed for `os.path.expanduser()` on non-Windows systems
             "FORCE_COLOR",  # force color output
             "NO_COLOR",  # disable color output
+            "NETRC", # used by pip and netrc modules
         ]
         if sys.stdout.isatty():  # if we're on a interactive shell pass on the TERM
             env.append("TERM")