BUG #17709: Regression in PG15 with window functions - "WindowFunc not found in subplan target lists"

The following bug has been logged on the website:

Bug reference: 17709
Logged by: Alexey Makhmutov
Email address: makhmutov(at)gmail(dot)com
PostgreSQL version: 15.1
Operating system: Ubuntu 20.04
Description:

Following query works fine on PG14, but produce error "WindowFunc not found
in subplan target lists" on PG15:

select 1
from
(
select count(case t1.a when 1 then 1 else null end) over (partition by
t2.b) c
from (select 1 a) t1, (select 1 b) t2
) t
where t.c = 1

On PG14 this query produce expected result (1), but on PG15.1 it produces
following error: "ERROR: WindowFunc not found in subplan target lists"
As of 8 December 2022, this problem could be reproduced on latest
REL_15_STABLE and HEAD (16dev) builds.

This seems to be result of functionality
https://github.com/postgres/postgres/commit/9d9c02ccd1aea8e9131d8f4edb21bf1687e40782
introduced in PG15.