use the captalized "ALLOW FILTERING" in the error message, because the
error message is a part of the user interface, it would be better to
keep it aligned with our document, where "ALLOW FILTERING" is used.
so, in this change, the lower-cased "allow filtering" error message is
changed to "ALLOW FILTERING", and the tests are updated accordingly.
see also a0ffbf3291
Refs #14321
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#15718
d43afd576e