As noted in issue #11979, Scylla inconsistently (and unlike Cassandra)
requires "IS NOT NULL" one some but not all materialized-view key
columns. Specifically, Scylla does not require "IS NOT NULL" on the
base's partition key, while Cassandra does.
This patch is a test which demonstrates this inconsistency. It currently
passes on Cassandra and fails on Scylla, so is marked xfail.
Refs #11979
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes#11980
e4dba6a830