sqlite3: `fetchmany` doesn't reject negative size

[ever0de]

Current Problem:

cursor.fetchmany(-3)  # ← Should reject negative
# Current: Accepts it
# Expected: Raise ValueError

Actual Test Result:

ERROR: fetchmany accepted -3, should raise ValueError

Test Code:

def test_invalid_fetchmany(self):
    self.assertRaises(ValueError, cursor.fetchmany, -3)

Affected Tests (1 test):

• test_sqlite3/test_dbapi.py::CursorTests::test_invalid_fetchmany

[ever0de]

RustPython#7240