When a node without the required feature attempts to join a Raft-based
cluster with the feature enabled, there is a race between the join
rejection response ("Feature check failed") and the ban notification
("received notification of being banned"). Depending on timing, either
message may appear in the joining node's log.
This starts to happen after 39cec4a (which introduced informing the
nodes about being banned).
Updated the test to accept both error messages as valid, making the test
robust against this race condition, which is more likely in debug mode
or under slow execution.
Fixes: scylladb/scylladb#27603
No backport: This failure is only present in master.
Closesscylladb/scylladb#27760