Just want to add newer version of Python and PyQt to our test runs. Also undoes a pin to a flake8 dependency that was only needed for python 3.7 and below. Leaves the PyQt 5.12.3 testing in place since the Designer/custom widget problem is still an issue for PyQt versions greater than that.
Context
Just want to add newer version of Python and PyQt to our test runs. Also undoes a pin to a flake8 dependency that was only needed for python 3.7 and below. Leaves the PyQt 5.12.3 testing in place since the Designer/custom widget problem is still an issue for PyQt versions greater than that.