fix(test): wait for track-name update in assertPlayer

[teancom]

A couple tests added in #314 would only intermittently pass (almost always locally, very flaky in CI). This should fix that, if my robot sidekick is right (it worked well locally, but so did the first version).

[seadowg]

@teancom looks good! We'll most likely want to prefer "wait" assertions over immediate ones as ComposeTestRule is only synchronized with the UI thread (details here if you're interested) and the app has a lot of event reaction logic that uses Flow either gets executed on a background thread or scheduled on the UI thread (giving the tests a window to assert before things have actually completed).

A nice trick if you spot a flake like this is to stick a Thread.sleep(1000) in before the flaky assertion, see if it passes every time, and if so then replace with a waitUntil or one of the async assertions like waitUntilAtLeastOneExists.