fix: flaky tests in CI

[armcknight]

By chance I noticed one of the tests flaking uses notifications (here), so wanted to try fixing all of them by adding XCTExpectations/waits for them to post before proceeding with assertions.

The temp commit forces them to run 50 times in both xcode 12/13, hopefully that would fail at least a couple times if this doesn't fix the flakiness.

Possibly fixes #2062

#skip-changelog

[armcknight]

Running just the flaky test cases 50 times without a failure, maybe this is the fix https://github.com/getsentry/sentry-cocoa/runs/7982082603?check_suite_focus=true

[armcknight]

OK so that didn't work: https://github.com/getsentry/sentry-cocoa/runs/7982225398?check_suite_focus=true

Looking at what tests run before it that may leave dirtied state that corrupts these tests.

[philipphofmann]

@armcknight, what is the current state of this PR? Do you need any input?

[armcknight]

@philipphofmann I'm stumped here currently, haven't circled back to look at what state could be getting corrupted before these tests run.

[philipphofmann]

I don't understand why the tests fail in CI and not locally. If the state would be a real problem, the tests should also fail locally sometimes.

[armcknight]

Closing this as I haven't had time to look at it. Can always resurrect the effort later.