Add flake8-pep585 dev dependency
Add `flake8-pep585` dev dependency so that our CI `flake8` checks that no deprecated type from `typing` is used, as established by [PEP 585](https://peps.python.org/pep-0585/).

Fix #1808.

CC: @severo 
Add flake8-pep585 dev dependency: Add `flake8-pep585` dev dependency so that our CI `flake8` checks that no deprecated type from `typing` is used, as established by [PEP 585](https://peps.python.org/pep-0585/).

Fix #1808.

CC: @severo 