sql: typechecking values clauses with tuples containing nulls is inconsistent with Postgres

[jordanlewis]

The following expression fails to typecheck in CockroachDB, but succeeds in Postgres:

VALUES((1, 2)), ((1, NULL))

CockroachDB:

demo@127.0.0.1:26257/defaultdb> values((1, 2)), ((1, null));

ERROR: VALUES types tuple{int, unknown} and tuple{int, int} cannot be matched
SQLSTATE: 42804

Postgres:

jordan=> values((1, 2)), ((1, null));
 column1
---------
 (1,2)
 (1,)
(2 rows)

Jira issue: CRDB-22279