pgsql: Remove use of deprecated containment operators in tests

Remove use of deprecated containment operators in tests

Switch @ to <@ and ~ to @> in gist-related tests.  The old operator
names have been deprecated and will eventually (possibly soon) be
removed.

Author: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://www.postgresql.org/message-id/flat/20201027032511.GF9241@telsasoft.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/3165426e54df02a6199c0a216546e5095e875a0a

Modified Files
--------------
src/test/regress/expected/create_am.out    | 10 +++++-----
src/test/regress/expected/create_index.out | 24 ++++++++++++------------
src/test/regress/sql/create_am.sql         |  4 ++--
src/test/regress/sql/create_index.sql      | 12 ++++++------
4 files changed, 25 insertions(+), 25 deletions(-)