BUG #18517: Dropping a table referenced by an initially deferred foreign key fails with an error

The following bug has been logged on the website:

Bug reference: 18517
Logged by: Alexander Lakhin
Email address: exclusion(at)gmail(dot)com
PostgreSQL version: 17beta1
Operating system: Ubuntu 22.04
Description:

The following script:
CREATE TABLE pkt (id int PRIMARY KEY);
CREATE TABLE fkt (id int PRIMARY KEY, fk int REFERENCES pkt INITIALLY
DEFERRED);
INSERT INTO pkt VALUES (1);
BEGIN;
INSERT INTO fkt VALUES (101, 1);

DROP TABLE pkt CASCADE;
COMMIT;

fails on commit with a weird error:
ERROR: relation 16390 has no triggers

BACKTRACE:
afterTriggerInvokeEvents at trigger.c:4700:7
AfterTriggerFireDeferred at trigger.c:5224:6
CommitTransaction at xact.c:2219:8
CommitTransactionCommandInternal at xact.c:3169:18
CommitTransactionCommand at xact.c:3099:9
finish_xact_command at postgres.c:2783:3
exec_simple_query at postgres.c:1299:4
PostgresMain at postgres.c:4684:27
BackendInitialize at backend_startup.c:123:1
postmaster_child_launch at launch_backend.c:269:9
BackendStartup at postmaster.c:3593:8
ServerLoop at postmaster.c:1677:10
PostmasterMain at postmaster.c:1372:11
startup_hacks at main.c:217:1

afterTriggerInvokeEvents() coding is:
/*
* So let's fire it... but first, find the correct relation
if
* this is not the same relation as before.
*/
if (rel == NULL || RelationGetRelid(rel) !=
evtshared->ats_relid)
{
...
if (trigdesc == NULL) /* should not happen */
elog(ERROR, "relation %u has no triggers",
evtshared->ats_relid);

Reproduced on REL_12_STABLE .. master.