:construction_worker: Drop 3.4 from build matrix
:construction_worker: Drop 3.4 from build matrix

3.4 is not available on Ubuntu 20.04 (see https://github.com/actions/python-versions/blob/main/versions-manifest.json).

Reverted specific version of 3.5 to just '3.5' which should be
available.

bigjason/django-choices,sergei-maertens/django-choices