Adapt dump() behavior to match ast.dump() on Python 3.9+ In Python 3.9+, ast.dump() omits optional fields/attributes from the output if their value is None. Such defaults are defined as class attributes.
See https://bugs.python.org/issue36287 And https://github.com/python/cpython/pull/18843
This patch does not change the output on previous Python versions, because the class attributes are missing there.
tests: Skip test_files() on Python >= 3.11 Given functions from astunparse are now mostly "battery included" in Python 3.10 and ongoing und the test itself is only a small part of the testing I think it's o.k. to simply skip now this test until upstream will probably do some adjustment.
