PG 14 - can't upgrade from a database using an aggregate with anyelement and anyarray

Hello,

this aggregate can be created without problems on PG 13 and before:

CREATE AGGREGATE array_accum(anyelement) (
SFUNC = array_append,
STYPE = anyarray,
INITCOND = '{}'
);

However, that fails with PG 14beta1 because array_append's parameter are now (anycompatiblearray, anycompatible) while it used to be (anyarray, anyelement).

I guess this is a side-effect of:

Allow some array functions to operate on a mix of compatible data
types (Tom Lane)

The functions are array_append() array_prepend(), array_cat(),
array_position(), array_positions(), array_remove(), array_replace(),
and width_bucket(). Previously only identical data types could be
used.

On a database with the above aggregate, pg_upgrade fails with the following error:

pg_restore: creating AGGREGATE "public.array_accum("anyelement")"
pg_restore: while PROCESSING TOC:
pg_restore: from TOC entry 2646; 1255 16552 AGGREGATE array_accum("anyelement") thomas
pg_restore: error: could not execute query: ERROR: function array_append(anyarray, anyelement) does not exist
Command was: CREATE AGGREGATE "public"."array_accum"("anyelement") (
SFUNC = "array_append",
STYPE = "anyarray",
INITCOND = '{}'
);

The problem is, that the version that works in PG 14:

CREATE AGGREGATE array_accum(anycompatible) (
SFUNC = array_append,
STYPE = anycompatiblearray,
INITCOND = '{}'
);

can't be created in PG 13 in preparation of the upgrade.

So the database can't be upgraded using pg_upgrade.

I am using PG14beta1 on Windows 10

Any ideas?
Thomas