GitLab

Summary:
- Moving the unit test scripts from .circleci to .github
- Remove docker file for unit test base
- Use the Conda from Docker image in Linux jobs.

Remaining follow-up items

- Reuse the unittest script in Linux GPU job like done in Linux CPU job.

The unit test script needs to be fixed to be used for Linux GPU job
in new GHA workflow. Keeping it as a separate follow-up work item.

Pull Request resolved: https://github.com/pytorch/audio/pull/3407

Differential Revision: D46498263

Pulled By: mthrok

fbshipit-source-id: d8256717a55bb4257151d819d3b2ebd453601eac

Summary:
As discussed in the [Torchaudio Migration Proposal](https://docs.google.com/document/d/1PF8biwiGzsjzfEBM78mlLiRrkcsGsvuYkeqkI66Ym8A/edit), this PR moves the Linux CPU unittest job to Nova tooling. Note that this does not disable the existing CircleCI job at the moment.

Passing Job: https://github.com/pytorch/audio/actions/runs/4986115298/jobs/8926499354?pr=3323

Pull Request resolved: https://github.com/pytorch/audio/pull/3323

Reviewed By: atalman, mthrok

Differential Revision: D46113506

Pulled By: osalpekar

fbshipit-source-id: 1778c360e17b9d02c63bcc60100834c75798d380