Attached a patch to fix as well. If the patch looks good to you, can you consider getting this to PG 15?
-- some basic examples from src/test/regress/sql/create_am.sql
CREATE TABLE heaptable USING heap AS
SELECT a, repeat(a::text, 100) FROM generate_series(1,9) AS a;
CREATE ACCESS METHOD heap2 TYPE TABLE HANDLER heap_tableam_handler;
CREATE MATERIALIZED VIEW heapmv USING heap AS SELECT * FROM heaptable;
-- altering MATERIALIZED
ALTER MATERIALIZED VIEW heapmv SET ACCESS METHOD heap2;
ALTER MATERIALIZED VIEW heapmv SET ACCESS METHOD heap;
-- setup event trigger
CREATE OR REPLACE FUNCTION empty_event_trigger()
RETURNS event_trigger AS $$
DECLARE
BEGIN
END;
$$ LANGUAGE plpgsql;
CREATE EVENT TRIGGER empty_triggger ON sql_drop EXECUTE PROCEDURE empty_event_trigger();
-- now, after creating an event trigger, ALTER MATERIALIZED VIEW fails unexpectedly
ALTER MATERIALIZED VIEW heapmv SET ACCESS METHOD heap2;
ERROR: unexpected command tag "ALTER MATERIALIZED VIEW"