Hold extract to the catalog call in the transform test, not to the DuckDB tree

[tamnd]

#2968 made the PostgreSQL transform read extract(field from x) as pg_catalog.extract('field', x), the way PostgreSQL 14 and later do. The DuckDB transform still reads it as date_part('FIELD', x), and the test that holds the two transforms to the same tree had an extract in its list, so cargo test -p rudb-pgparse --test transform has failed since. The release gate stops on it, which is one of the two tests that kept 0.10.7 off crates.io.

The statement in the list keeps everything but the extract, and a test of its own checks that the new transform makes the catalog call with the field in lower case. The rest of that statement was compared against the failing output on server3 and builds the same tree in both.