Update the pysat cap.

[aburrell]

Is your feature request related to a problem? Please describe.
It can be difficult to support older versions for a long time. Pysat deprecates a lot of things in v3.2.0, so that would be a good updated cap.

Describe the solution you'd like
In a future version, set a cap for pysat support to a minimum of 3.2.0 or higher.

Describe alternatives you've considered
Maintaining all current versions and adding more CI testing

Additional context
Unit tests have many version checks and this makes things complicated to maintain.