Drop OSX from testing matrix

[mikemhenry]

For now I am going to drop OSX from the testing matrix, openmm_rbfe/OpenFE_showcase_1_RBFE_of_T4lysozyme.ipynb & showcase/openfe_showcase.ipynb times out

=================================== FAILURES ===================================
_______ openmm_rbfe/OpenFE_showcase_1_RBFE_of_T4lysozyme.ipynb::Cell 27 ________
[gw0] darwin -- Python 3.10.14 /Users/runner/micromamba/envs/openfe-notebooks/bin/python
Notebook cell execution failed
Cell 27: Timeout of 2000 seconds exceeded while executing cell. Failed to interrupt kernel in 5 seconds, so failing without traceback.

Input:
# complex dry-run
complex_unit = list(complex_dag.protocol_units)[0]

complex_unit.run(dry=True, verbose=True)

___________________ showcase/openfe_showcase.ipynb::Cell 27 ____________________
[gw2] darwin -- Python 3.10.14 /Users/runner/micromamba/envs/openfe-notebooks/bin/python
Notebook cell execution failed
Cell 27: Timeout of 2000 seconds exceeded while executing cell. Failed to interrupt kernel in 5 seconds, so failing without traceback.

Input:
# complex dry-run
complex_unit = list(complex_dag.protocol_units)[0]

complex_unit.run(dry=True, verbose=True)

=========================== short test summary info ============================
FAILED openmm_rbfe/OpenFE_showcase_1_RBFE_of_T4lysozyme.ipynb::Cell 27
FAILED showcase/openfe_showcase.ipynb::Cell 27
======= 2 failed, 203 passed, 9 skipped, 5 xfailed in 2110.16s (0:35:10) =======

[mikemhenry]

I will keep this issue since I rather skip testing the last few cells on OSX than drop it forever