Improve lint Github Action

[crasanders]

Our Github action is supposed to perform linting but it's not configured correctly. Our code should be formatted using flake8 and black, and type-checked with mypy, but only the mypy checking is working correctly. flake8 warnings are being suppressed, and black isn't being used at all.

See the botorch workflows for an example of how this could work: https://github.com/pytorch/botorch/blob/main/.github/workflows/lint.yml