auth_test: Modify yet another case to use "normal" continuation.
auth_test: Modify yet another case to use "normal" continuation.

test_cassandra_hash also sort of expects exceptions. ASas causes false
positives here as well with seastar::thread, so do it with normal cont.
Message-Id: <9dec4ca83f1ae3c1f84c419abdc2341dc329ca09@scylladb.com>

duarten/scylla,kjniemi/scylla,scylladb/scylla,kjniemi/scylla,raphaelsc/scylla,raphaelsc/scylla,avikivity/scylla,raphaelsc/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,kjniemi/scylla