Test on an older Safari on BrowserStack

[Jaifroid]

We claim to support Safari >= 11.3, which is the first one that supports Service Workers. However, we can't unfortunately test ServiceWorker mode on Safari at all on BrowserStack because BrowserStack doesn't expose http://localhost on macOS or on iOS. Instead, the app runs from something like http://bs-local.com, which of course is insecure.

So, we have to run e2e tests in jQuery mode only on Safari on macOS. However, the test is currently running on Safari 14, which is higher than the minimum we claim to support. So, we should lower it and run it on an earlier OS like Catalina.

It might be worth seeing if it can be run on iOS as well.