TRUNCATE on Iceberg table gives `unknown database` error

[rad-pat]

When trying to truncate an table in an iceberg catalog, a strange error that the database is unknown is seen.

Steps to reproduce the behavior (Required)

1. SET CATALOG iceberg_catalog;
2. CREATE TABLE test_db.t1 (a INTEGER);
3. TRUNCATE TABLE test_db.t1

Expected behavior (Required)

Either truncate the table, if supported, or error suggesting that action is not yet supported - similar to DELETE (at this time)

Real behavior (Required)

SQL Error [5501] [3F000]: Unknown database 'test_db'

StarRocks version (Required)

4.0.2-1f1aa9c