Remove usage of codecov ATS feature

[Swatinem]

We are in the process of deprecating the ATS feature of codecov, and I saw you are one of the few (open source) users of it.

This PR removes the usage of ATS, just calling out to the whole testsuite all at once. I did keep some of the --collect logic for the codemod-tests CI job, as I believe this is doing some kind of testsuite splitting.

As I saw you have modified the CI related workflows fairly recently, I’m curious whether the ATS feature as it exists is providing any value to you?

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A completely unrelated comment, as I have looked at your other CI jobs as well, you are limiting mypy checks to only the changed files. However any changes to types can also have an effect on downstream importers, which also need to be typechecked. As those are skipped by the filtering to only changed files, this can cause type errors in subsequent PRs.

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