Bump reportlab 3.5→3.6, pillow 5→8
Bump reportlab 3.5→3.6, pillow 5→8

Pillow <6 had problems due to a CPython API deprecation which was
removed py3.10, but Pillow ≥6 brokke the old reportlab.
Luckily, reportlab 3.6 appears to work with pillow 8 judging by a
simple user sheet generation.

agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft