t: use test_grep in t3701 and t4055
As a preparatory clean-up, use the "test_grep" test utility instead of
regular "grep" which provides better debug information if tests fail.
Signed-off-by: Leon Michalak <leonmichalak6@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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