core: migrate code to benefit from 3.9 stuff

for now keeping ruff on 3.8 target version, need to sort out modules as well

my/core/pytest.py

@@ -2,7 +2,9 @@
 Helpers to prevent depending on pytest in runtime
 """
 
-from .internal import assert_subpackage; assert_subpackage(__name__)
+from .internal import assert_subpackage
+
+assert_subpackage(__name__)
 
 import sys
 import typing