CI Flake `test_no_delay`

[ddustin]

It appears #9065 introduced a flake into the CI. test_no_delay now intermittently fails with this assert failing:

        if expected_saving > 0.5:
            # Platform shows a meaningful Nagle effect: assert the full saving.
>           assert normal_time < nagle_time - expected_saving
E           assert 17.35592794418335 < (24.079977989196777 - 7.486647367477417)

Let's see if we can figure out a more consistent way to perform this nagle test 🤔

[ScuttoZ]

I proposed a fix in PR#9231 introducing a statistical margin instead of a fixed 0.5 expected saving