Add test for Item.claim with an unlimited quantity
Add test for Item.claim with an unlimited quantity

This test is similar to the tests added in 1c6d106. The difference is
that this test checks for an item with an unlimited quantity.

Just as with 1c6d106, a TODO is being added to address
`Item.quantity_claimed`.

dirn/Secret-Santa,dirn/Secret-Santa,dirn/Secret-Santa,dirn/Secret-Santa