Update Mypy to 0.950 (#70948)

Co-authored-by: J. Nick Koston <nick@koston.org>

script/hassfest/mypy_config.py

@@ -221,6 +221,8 @@ GENERAL_SETTINGS: Final[dict[str, str]] = {
     "warn_unused_configs": "true",
     "warn_unused_ignores": "true",
     "enable_error_code": "ignore-without-code",
+    # Strict_concatenate breaks passthrough ParamSpec typing
+    "strict_concatenate": "false",
 }
 
 # This is basically the list of checks which is enabled for "strict=true".