Cache lookup failure after dropping type used in partition column

[naisila]

What we fail to access is the distribution column and its type, because it is dropped from previous DROP TYPE comp_type CASCADE. The issue can be reproduced as follows:

SET citus.shard_count TO 4;

CREATE TYPE my_type AS (int_field int);
CREATE TABLE tbl (a my_type);
SELECT create_distributed_table('tbl', 'a');

-- the following should error out but it doesn't
-- it drops the distribution column of the table in the coordinator -- OOPS!
-- doesn't propagate anything to shards
DROP TYPE my_type CASCADE;
NOTICE:  drop cascades to column a of table tbl

-- OOPS no distribution column
\d+ tbl
               Table "public.tbl"
 Column | Type | Collation | Nullable | Default
--------+------+-----------+----------+---------

-- shards are still there!!
SELECT run_command_on_workers($$ SELECT json_agg(relname) FROM pg_class WHERE relname LIKE 'tbl%'$$);
                     run_command_on_workers
----------------------------------------------------------------
 (localhost,9701,t,"[""tbl"", ""tbl_102008"", ""tbl_102010""]")
 (localhost,9702,t,"[""tbl"", ""tbl_102009"", ""tbl_102011""]")
(2 rows)

SELECT * FROM citus_shards;
ERROR:  cache lookup failed for type 17132

DROP TABLE tbl;
ERROR:  cache lookup failed for type 17132

EDIT: problem already mentioned in https://github.com/citusdata/citus-enterprise/issues/687

Originally posted by @naisila in #5780 (comment)