cache lookup failed dropping public schema with trgm index

Hi,

This reproduces on 15.4 and 13.12:

create table foo(t text);
create extension pg_trgm;
create index on foo using gist(t gist_trgm_ops);
drop schema public cascade;

NOTICE:  drop cascades to 2 other objects
DETAIL:  drop cascades to table foo
drop cascades to extension pg_trgm
ERROR:  cache lookup failed for function 1195999
Time: 20.968 ms