Reset minimum deployment target and make GitHub Actions work #160

Work plan

• Study how https://github.com/fulldecent/swift6-module-template (inside the template folder) sets up its CI
• Study how Alamofire sets up its CI
• Setup CI here
• Run those steps manually (carefully ensuring your build environment matches what you expecte the test runner to have)
• Get those tests to pass locally before committing to try on CI