Adjust `test_service_levels_upgrade`: right before upgrade to topology
on raft, enable an error injection which triggers when the standard role
manager is about to query the legacy auth tables in the
system_auth keyspace. The preceding commit which fixes
scylladb/scylladb#24963 makes sure that the legacy tables are not
queried during upgrade to topology on raft, so the error injection does
not trigger and does not cause a problem; without that commit, the test
fails.
(cherry picked from commit 3a082d314c)
d9075e6160