Existing test improvements

[marc-white]

The following (relatively easy, non-controversial) updates should be made w.r.t. the existing test suite (https://github.com/PyWiFeS/pywifes/blob/main/tests/README.md):

• Fix the addresses of the test data checkouts. The git@ SSH addresses are account-protected; however, the HTTPS addresses aren't. Those should be used instead.
• Set up a GitHub action to run the full test suite. This should only be done for major events (pull requests, releases), given the size and time the test suite takes up.
• Fix the test failure caused by not setting the PYWIFES_DIR environment variable (this should gracefully fall back to the install reference_data directory like the package itself does).