array_cat anycompatible change is breaking xversion upgrade tests

crake is showing xversion upgrade failures since 9e38c2bb50:

pg_restore: error: could not execute query: ERROR: function array_cat(anyarray, anyarray) does not exist
Command was: CREATE AGGREGATE "public"."array_cat_accum"("anyarray") (
SFUNC = "array_cat",
STYPE = "anyarray",
INITCOND = '{}'
);

As was discussed in the thread leading up to that commit, modifying the
signature of array_cat and friends could break user-defined operators
and aggregates based on those functions. It seems to me that the
usability gain from this change is worth that cost, but it is causing
an issue for xversion tests.

I think the most plausible response is to add this aggregate to the filter
logic that already exists in the xversion tests. Perhaps we could
alternatively change this test case so that it relies on some other
polymorphic function, but I'm not quite sure what a good candidate
would be.

regards, tom lane