Change away from Karma for headless browser tests in CI

[Karma is being deprecated][kdep] and [shadow-cljs hasn't shown any movement to migrate away from it][silent-shadow]

[kdep]: https://www.npmjs.com/package/karma
[silent-shadow]: https://github.com/thheller/shadow-cljs/issues/1123

It looks like [Jasmine Browser Runner][jasmine] is probably the best choice to switch to.

[jasmine]: https://github.com/jasmine/jasmine-browser-runner