Test axum_factory::tests::test_supergraph_timeout fails if port 4000 is in use

[glasser]

The test axum_factory::tests::test_supergraph_timeout does not use an ephemeral port, so cargo test fails if port 4000 is in use (for example, if you just happen to be running a router with default configuration).

[abernix]

@nicholascioli Did you possibly fix this recently?

[nicholascioli]

Yes! This PR makes the router bind to a random port for the integration tests. Is this issue happening even after the linked change?