t3701: don't hard code sha1 hash values

t3701: don't hard code sha1 hash values

Use a filter when comparing diffs to fix the value of non-zero hashes
in diff index lines so we're not hard coding sha1 hash values in the
expected output. This makes it easier to change the expected output if
a test is edited as we don't need to worry about the exact hash value
and means the tests will work when the hash algorithm is transitioned
away from sha1.

Thanks-to: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>