t: use test_config in t4055
Use the modern "test_config" test utility instead of manual"git config"
as the former provides clean up on test completion.
This is a prerequisite to the commits that follow which add to this test
file.
Signed-off-by: Leon Michalak <leonmichalak6@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
authored by