tests: integration-shadow test fails after rand 0.9 upgrade

The upgrade to rand 0.9 in !2869 (merged) seems to have broken onion services in shadow simulations.

The test failure has been replicated locally by @jnewsome.

The plan is to either hold off on merging any new MRs to arti until it has been debugged and fixed, or to revert !2869 (merged).