BUG #19420: Zombie FK exists after partition is detached.

The following bug has been logged on the website:

Bug reference:      19420
Logged by:          Agnieszka Chodkowska
Email address:      a.chodkowska@gmail.com
PostgreSQL version: 16.6
Operating system:   Linux, Debian 12.2.0 64 bit
Description:

I have child table  with FK defined as folllows

ALTER TABLE IF EXISTS tst.child_test_1
    ADD CONSTRAINT child_test_1_parent_id_parent_part_by_fkey FOREIGN KEY
(parent_id, parent_part_by)
    REFERENCES tst.maintenance_test_1_p20260218 (id, part_by) MATCH SIMPLE
    ON UPDATE NO ACTION
    ON DELETE CASCADE;

I updated configuration according to documentation as follows:
retention_keep_table=false ,
retention_keep_index = false

Somehow postgresql retains the foreign keys of the detached/dropped
partitions, to the parent table partitions.

I try the following methods:
partman.run_maintenance('tst.child_test_1')
partman.run_maintenance()
ALTER TABLE tst.child_test_1 DETACH PARTITION <child_test_p_20260218>

The error persisted regardless of the method used.