Need CI to test package publishing workflow

[IshaanDesai]

The package publishing workflow is run every time a release is made. If changes to the workflow or package setup are done, the way to test the workflow is by doing a release candidate. This is a cumbersome way to test the publishing workflow. It would be better to have a workflow which publishes to TestPyPI every time a release PR is opened, and only when it passes, the release is allowed.