gio/tests/g-file-info: don't assume million-in-one events don't happen
The modification time test creates a file, gets the modification time in seconds, then gets the modification time in microseconds and assumes that the difference between the two has to be above 0.
As rare as this may be, it can happen:
$ stat g-file-info-test-50A450 -c %y 2021-07-06 18:24:56.000000767 +0100
Change the test to simply assert that the difference not negative to handle this case.