BUG #19026: ResourceOwnerForget can't find owner for invalid plancache

The following bug has been logged on the website:

Bug reference: 19026
Logged by: Alexander Lakhin
Email address: exclusion(at)gmail(dot)com
PostgreSQL version: 18beta3
Operating system: Ubuntu 24.04
Description:

The following script:
create function part_hashint4_noop(value int4, seed int8)
returns int8 as $$
create table t();
select value + seed;
$$ language sql strict immutable parallel safe;

create operator class part_test_int4_ops for type int4 using hash as
function 2 part_hashint4_noop(int4, int8);

create table pt(i int) partition by hash (i part_test_int4_ops);
create table p1 partition of pt for values with (modulus 4, remainder 0);

insert into pt values (1);
insert into pt values (1);

triggers an expected error and then an internal one:
ERROR: CREATE TABLE is not allowed in a non-volatile function
CONTEXT: SQL function "part_hashint4_noop" statement 1

ERROR: XX000: plancache reference 0x643ae41a7d98 is not owned by resource
owner Portal
CONTEXT: SQL function "part_hashint4_noop" during startup
LOCATION: ResourceOwnerForget, resowner.c:618

I also encountered a gibberish owner name (with more complicated queries)
like:
2025-08-19 16:32:22.878 EEST|postgres|regress002|68a47cdb.2d8921|ERROR:
plancache reference 0x5d56f0675c50 is not owned by resource owner
?^O^^?H??^H?????H??^H??^O^^?AUATUSH??^HI??H?w(H?=??

Reproduced starting from 0313c5dc6.