test(duckdb): add test for supporting fixed-size array types (#9855)

These are already supported automatically through sqlglot, just adding a
test here. Fixes #7963.

One open question: currently these are cast to variable-length lists in
`to_pyarrow` (matching the existing behavior of `dt.Array` types), but
it could be argued that we should pass them through as fixed-length
lists instead. This would require a bit of work, but nothing too tricky.

ibis/backends/duckdb/tests/test_datatypes.py

@@ -36,6 +36,7 @@
             ("UUID", dt.uuid),
             ("VARCHAR", dt.string),
             ("INTEGER[]", dt.Array(dt.int32)),
+            ("INTEGER[3]", dt.Array(dt.int32)),
             ("MAP(VARCHAR, BIGINT)", dt.Map(dt.string, dt.int64)),
             (
                 "STRUCT(a INTEGER, b VARCHAR, c MAP(VARCHAR, DOUBLE[])[])",