Ensure context is set when testing lot quantity

Since changeset 3a17f8e704a7, there is no more context leak so the context when
computing quantities is exactly the one at the instantiation.

review25231002

tests/test_stock_lot.py

@@ -112,6 +112,7 @@ class StockLotTestCase(ModuleTestCase):
                     (storage.id, product.id, None): 3,
                     })
             with Transaction().set_context(locations=[storage.id]):
+                lot1, lot2 = Lot.browse([lot1, lot2])
                 self.assertEqual(lot1.quantity, 5)
                 self.assertEqual(lot2.quantity, 8)