Enable Swift SDK testing in GitHub Action CI runs

When porting from TravisCI to GitHub Actions, I gave up on getting the Swift SDK tests to run.

If/when we get back to this again, be sure to look at https://github.com/apache/openwhisk-runtime-swift/blob/ac1234e92b27afc0708a44bbac3081ba74ca0420/tools/travis/deploy.sh to replicate the special way the entire OpenWhisk system was deployed to use the locally built Swift runtime images.

