Drive-by flaky test fix

[sanchda]

Statix tests can flake out on machines with a Datadog agent, since they can erroneously bind to the typical UDP port (8125) and then respond to traffic intended for a different destination. It would be possible to isolate the tests to their own network namespace, but just jiggling the port is a fairly common, no-dep solution.

Example flake:

  1) test measure/2,3 (StatixTest)
     test/statix_test.exs:119
     Unexpectedly received message {:test_server, %{host: {127, 0, 0, 1}, port: 37861, socket: #Port<0.6>}, "datadog.trace_agent.trace_writer.traces:0|c|#version:7.58.2\n"} (which matched _any)
     code: refute_received _any
     stacktrace:
       test/statix_test.exs:137: (test)