Tests: Ignore TableUnknownException in test_graceful_stop_concurrent_queries
Tests: Ignore TableUnknownException in test_graceful_stop_concurrent_queries

This is a temporary band-aid to avoid flaky test failures until we've a
proper fix in place.

EvilMcJerkface/crate,EvilMcJerkface/crate,EvilMcJerkface/crate,crate/crate,crate/crate,crate/crate