Python 3.4 is no longer supported by upstream, and various things like Github Actions don't support it. If we also end up dropping support for Python 2, then Python 3.4 would also hold up using type annotations syntax if we ever want to use it (see #225 for old work on that, using comment syntax).

I propose we drop it from setup.cfg classifiers, setup.py python_requires and CI in master (which will become a breaking change release, pluggy 1.0.0).