Codecov ATS action should ship dependancies and not require them to be setup manually

[rohan-at-sentry]

What product do you want to improve? Codecov ATS Github Action Is your feature request related to a problem? Please describe. Some projects use pipenv to install dependencies, so pytest is never actually installed globally on the Github Action machine. In this scenario, the ATS Github Action experiences an error because pytest isn't ever found.

Describe the solution you'd like Ship action with pytest and other dependencies.

Describe alternatives you've considered N/A Additional context From customer using ATS for Python (beta)