Fix type check

Author: abravalheri

setuptools/compat/py312.py

@@ -1,9 +1,11 @@
+from __future__ import annotations
+
 import sys
 
 if sys.version_info >= (3, 12, 4):
     # Python 3.13 should support `.pth` files encoded in UTF-8
     # See discussion in https://github.com/python/cpython/issues/77102
-    PTH_ENCODING = "utf-8"
+    PTH_ENCODING: str | None = "utf-8"
 else:
     from .py39 import LOCALE_ENCODING