Assert failure when using CTAS USING iceberg in PL/pgSQL

[sfc-gh-mslot]

The following triggers an assert failure in SPI:

CREATE OR REPLACE FUNCTION test_ctas_iceberg()
  RETURNS void
  LANGUAGE plpgsql
  AS $$
  BEGIN
      EXECUTE 'CREATE TABLE test_iceberg USING iceberg AS SELECT 1 AS id';
  END;
  $$;
select test_ctas_iceberg();
server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
The connection to the server was lost. Attempting reset: Failed.
Time: 523.348 ms

In the log:

TRAP: failed Assert("ctastmt->if_not_exists || ctastmt->into->skipData"), File: "spi.c", Line: 2750, PID: 51995
0   postgres                            0x00000001005fb070 ExceptionalCondition + 108
1   postgres                            0x00000001003331ec _SPI_execute_plan + 2004
2   postgres                            0x00000001003332f0 SPI_execute_extended + 188
3   plpgsql.dylib                       0x0000000101afe95c exec_stmts + 2012
4   plpgsql.dylib                       0x0000000101afda94 exec_stmt_block + 912
5   plpgsql.dylib                       0x0000000101afb760 plpgsql_exec_function + 608
6   plpgsql.dylib                       0x0000000101b0d66c plpgsql_call_handler + 320
7   postgres                            0x00000001002ef5cc ExecInterpExpr + 1472
8   postgres                            0x000000010032879c ExecResult + 324
9   postgres                            0x00000001002f7b48 standard_ExecutorRun + 292
10  pg_stat_statements.dylib            0x000000010103133c pgss_ExecutorRun + 184
11  pgaudit.dylib                       0x0000000105ee6170 pgaudit_ExecutorRun_hook + 36
12  postgres                            0x00000001004cc538 PortalRunSelect + 232
13  postgres                            0x00000001004cc164 PortalRun + 492
14  postgres                            0x00000001004cb138 exec_simple_query + 1396
15  postgres                            0x00000001004c8d38 PostgresMain + 3496
16  postgres                            0x00000001004c42a4 BackendInitialize + 0
17  postgres                            0x00000001004292b0 PgArchShmemSize + 0
18  postgres                            0x000000010042d818 ServerLoop + 7312
19  postgres                            0x000000010042b300 InitProcessGlobals + 0
20  postgres                            0x000000010034b6dc help + 0
21  dyld                                0x000000018a3c9d54 start + 7184

looks somewhat like a Postgres bug, but does get triggered by our AST manipulation