Derive mypy python_version from REQUIRED_PYTHON_VER (#62616)

script/hassfest/mypy_config.py

@@ -7,6 +7,8 @@ import os
 from pathlib import Path
 from typing import Final
 
+from homeassistant.const import REQUIRED_PYTHON_VER
+
 from .model import Config, Integration
 
 # Modules which have type hints which known to be broken.
@@ -143,7 +145,7 @@ HEADER: Final = """
 """.lstrip()
 
 GENERAL_SETTINGS: Final[dict[str, str]] = {
-    "python_version": "3.8",
+    "python_version": ".".join(str(x) for x in REQUIRED_PYTHON_VER[:2]),
     "show_error_codes": "true",
     "follow_imports": "silent",
     # Enable some checks globally.