BUG #19098: Can't create unique gist index, where pg_indexes says that WITHOUT OVERLAPS does exacly that

The following bug has been logged on the website:

Bug reference:      19098
Logged by:          Bartłomiej Nowak
Email address:      n.bartek3762@gmail.com
PostgreSQL version: 18.0
Operating system:   Linux pop-os x86_64
Description:        

Using unique constraint, at Postgres 18, I am able to use `WITHOUT OVERLAPS`
using that, in fact I created index, that I can see at pg_indexes:
`CREATE UNIQUE INDEX inventoryoffer_unique_index ON public.test_table USING
gist (inventory_id, account_id, from_offer_id, for_account_id,
_availability_range);`
It says, that it is gist UNIQUE index.
But if I would like to just create index like that (copy and paste that
definition from pg_indexes)
I am getting error:
[0A000] ERROR: access method "gist" does not support unique indexes
which sounds weird, in fact of `WITHOUT OVERLAPS` existence