spanstat: fix flakey test case.
spanstat: fix flakey test case.

This test case fails often when running this test.
Add small sleep duration to ensure that second measure
can be identified as distinct from first.

Signed-off-by: Tom Hadlaw <0fde47a586f3fe1b62983bf113d5231aee2fb6c9@isovalent.com>

cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium