`package-dir` input of the GitHub Action shouldn't imply building only from a Git checkout

[webknjaz]

Description

$sbj. https://github.com/pypa/cibuildwheel/blob/a4f8eb3/action.yml#L5 says it's a dir. But it's actually passed in place where an sdist would work too https://github.com/pypa/cibuildwheel/blob/a4f8eb3/action.yml#L40.

Build log

No response

CI config

No response

[joerick]

We can rename the option to package and update the docs but we'd need to be really careful to keep package-dir working. The action.yml isn't tested in CI and a lot of workflows would break if we got that wrong!