t/helper: use correct object hash in partial-clone helper

t/helper: use correct object hash in partial-clone helper

The `object_info()` function of the partial-clone helper is responsible
for checking the object ID of a repository other than `the_repository`.
We use `parse_oid_hex()` in this function though, which means that we
still depend on `the_repository->hash_algo`.

Fix this by using the object hash of the function-local repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>