Add test step to cibuildwheel.

[carlosperate]

Looking into adding tests (issue https://github.com/pyocd/libusb-package/issues/19), and it looks like we can run a test step in cibuildwheel after each wheel is built, simple! 🥳 https://cibuildwheel.readthedocs.io/en/v2.16.2/options/#testing

So I've added pyusb as a test requirement and it runs python test.py.

• Is that the best current way to test the wheels?
• Is there something else this should do?

I was planning to add this as part of PR https://github.com/pyocd/libusb-package/pull/20, but unfortunately the tests are failing on Linux, so I didn't want that to be a blocker for that PR.

This PR is running on top of the main branch without any other modifications, to test the current wheels, which I assume should be working.

Test result from my fork: https://github.com/carlosperate/libusb-package/actions/runs/6975861223/job/18983558875

Building cp37-manylinux_x86_64 wheel
CPython 3.7 manylinux x86_64
...
  Collecting pyusb
    Downloading pyusb-1.2.1-py3-none-any.whl (58 kB)
       ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 58.4/58.4 kB 4.8 MB/s eta 0:00:00
  Installing collected packages: pyusb
  Successfully installed pyusb-1.2.1
      + mkdir -p /tmp/tmp.G43sXfIgjj/test_cwd
      + sh -c 'python /project/test.py'
  Path to included library: /tmp/tmp.G43sXfIgjj/venv/lib/python3.7/site-packages/libusb_package/libusb-1.0.so
  Unable to load libusb backend!

https://github.com/pyocd/libusb-package/blob/7a62b644f3cc075a37e8d2e255ee9941ce2ca752/test.py#L13-L17 https://github.com/pyocd/libusb-package/blob/7a62b644f3cc075a37e8d2e255ee9941ce2ca752/src/libusb_package/init.py#L66-L87