Run the tests in CI

[hisaac]

CI currently runs mise run build only. Once a test target exists, it should run the tests too.

Notes

• The build task calls xcodebuild build. Tests need xcodebuild test with the test scheme, so this
  is probably a second mise task rather than a change to the existing one — keeping a plain build
  available is useful.
• The raw log tee should cover the test run as well, for the same reason it exists for builds.
• If the integration tests move the real cursor, check how that behaves on a headless runner before
  assuming it works. That may decide whether integration tests run on every push or only on demand.
• Consider whether a test failure should block the existing build job or run alongside it.