Mac OSX Tests for torch==1.9.1 fail when installing dependencies

[nickfraser]

Noticed in tests for #956, when OS=macosx-latest & torch==1.9.1, pip fails find the necessary dependencies (specifically, torch==1.9.1). It is particularly weird because manually searching pypi.org shows that this build does indeed exist. Specifically, I believe that torch-1.9.1-cp38-none-macosx_10_9_x86_64.whl should get installed.
Even more weird, 1.9.0 is suggested as an installation candidate, despite not listing any extra builds.

Not sure if there is some temporary bug with Pypi (in which case, this might resolve itself). Or if this build has been yanked somehow (they don't appear to be!) Alternatively, we could remove this from the test list for Mac OSX, or move back to torch==1.9.0.

Example test output:

nox > Command python -m pip install torch==1.9.1 failed with exit code 1:
ERROR: Could not find a version that satisfies the requirement torch==1.9.1 (from versions: 1.9.0, 1.10.0, 1.10.1, 1.10.2, 1.11.0, 1.12.0, 1.12.1, 1.13.0, 1.13.1, 2.0.0, 2.0.1, 2.1.0, 2.1.1, 2.1.2, 2.2.0, 2.2.1, 2.2.2, 2.3.0)
ERROR: No matching distribution found for torch==1.9.1
nox > Session tests_brevitas_cpu-3.8(jit_disabled, pytorch_1.9.1) failed.

[Giuseppe5]

Related to #906

[nickfraser]

In fact, a duplicate!

[nickfraser]

Alternatively, we can move the tests to python=3.9, python=3.10, since python=3.8 is reaching EOL soon.

It seems this won't help.