Changes for 8.1.1 (openmm#4376)

Fixes to Python API for ATMForce (openmm#4319)

Updated version number to 8.1 (openmm#4250)

Fixed errors in Python wrapper for AmoebaVdwForce (openmm#3923)

Fixed exceptions in benchmark script (openmm#3912)

Updated version number to 8.0 (openmm#3795)

* Updated version number to 8.0

Cleanup Conda Env on Mac Mini (openmm#3371)

* Try older miniforge version

Use miniforge version that was known to be working

* ci bump

* switch back to using latest miniforge3 + cleanup miniconda folder at the end of testing for the self-hosted runner'

* ci bump

* ci bump

Fixed error using AMOEBA 2018 with RNA (openmm#3313)

Fixed an error in condensing LJ types in CharmmPsfFile (openmm#3210)

Fixed an error in condensing LJ types in CharmmPsfFile (openmm#3210)