alternator-test: add a test for wrong BEGINS_WITH target type
alternator-test: add a test for wrong BEGINS_WITH target type

The test ensures that passing a non-compatible type to BEGINS WITH,
e.g. a number, results in a validation error.
Tested both locally and remotely.
Message-Id: <15394c3195c1adaaa8423f912179fa314d90f143@scylladb.com>

scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla