fix(db-dtypes): Drop support for Python <= 3.9#16966

chalmerlowe wants to merge 6 commits intomaingoogleapis/google-cloud-python:mainfrom

feat/drop-python-3.7-3.9-db-dtypesgoogleapis/google-cloud-python:feat/drop-python-3.7-3.9-db-dtypesCopy head branch name to clipboard