tests: Handle a few test failures on MoltenVK.
Commit "Dispatch just four invocations..." doesn't handle a test failure. The test was already correct, the additional threads would just do nothing at all, but after the change it's more sensible.
Commit "Dispatch just four invocations..." doesn't handle a test failure. The test was already correct, the additional threads would just do nothing at all, but after the change it's more sensible.