Wait longer for the macOS test fixture to stop running

[twometresteve]

Goal

Attempt to reduce test flakes by waiting longer for crash reports to be written.

Design

I've noticed some test flakes recently where internal errors were being sent to Maze Runner due to invalid (truncated) crash report files. It seem that the lsappinfo mechanism we were using to detect the app stopping running was not reliably giving enough time for crash reports to be written, so I have fallen back to a simple wait instead.

Testing

Before this change, I could hardly get the RecrashObjcMachScenario to pass at all - after the change it passed 20/20 times. The down side of this change is that does increase the length of test runs from about 20 to 24 minutes.

[github-actions]

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