tests: Add some rounding tolerance in timeout test

Occasionally this test fails in CI with the message:

assertion failed: (current_time / 1000000 - last_time / 1000000 == 1)

The way this calculation is done at the moment, a difference of 1001ms between current_time and last_time can result in failure, if the times are close to a multiple to 1000ms.

Change it to only truncate the result after doing the subtraction, and add a 500ms tolerance to account for scheduling delays in the test. (For example, the test_func() could be called, then descheduled before it gets to call g_get_monotonic_time().

Additionally, change the test to use g_assert_cmpint() so that future failures provide more useful debug information.

Signed-off-by: Philip Withnall pwithnall@endlessos.org