further tolerance relaxing for s390x
While investigating Ubuntu autopkgtest failures, I found that tests on s390x can exhibit a similar tolerance failure to the ones recently patched. This MR adds another tolerance adjustment to accommodate s390x.
Log of this case:
>       assert_norms(
            mesh.cell_circumradius,
            [2.3626166467239324e02, 8.2555845809410222e00, 5.4304737796772495e-01],
            1.0e-15,
        )
...
E       AssertionError: Norms don't coincide.
E       Expected: [2.3626166467239324e+02, 8.2555845809410222e+00, 5.4304737796772495e-01]
E       Computed: [2.3626166467239324e+02, 8.2555845809410258e+00, 5.4304737796772429e-01]