Possible intermittent failure in tor_guardmgr::sample::test::sample_test

It looks like we have a random failure in this test. I haven't been able to reproduce this, but I'll run it in a look to see if it will come up again.

---- sample::test::sample_test stdout ----
thread 'sample::test::sample_test' panicked at 'assertion failed: samples[0] != samples[1] || samples[1] != samples[2]', crates/tor-guardmgr/src/sample.rs:813:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    sample::test::sample_test