BUG #19000: gist index returns inconsistent result with gist_inet_ops

The following bug has been logged on the website:

Bug reference: 19000
Logged by: Alexander Lakhin
Email address: exclusion(at)gmail(dot)com
PostgreSQL version: 18beta2
Operating system: Ubuntu 24.04
Description:

The following script:
CREATE EXTENSION btree_gist;

CREATE TABLE t AS SELECT '192.168.1.0/25'::inet AS i;

SELECT * FROM t WHERE i << '192.168.1.0/24'::cidr;
i
----------------
192.168.1.0/25

CREATE INDEX ON t USING gist(i);

SELECT * FROM t WHERE i << '192.168.1.0/24'::cidr;
i
---
(0 rows)

shows an inconsistency when using the "<<" operator with a gist index.

Reproduced starting from be1cc9aaf.