leak tests: mark some misc tests as passing with SANITIZE=leak

leak tests: mark some misc tests as passing with SANITIZE=leak

Mark some tests that match "*{mktree,commit,diff,grep,rm,merge,hunk}*"
as passing when git is compiled with SANITIZE=leak. They'll now be
listed as running under the "GIT_TEST_PASSING_SANITIZE_LEAK=true" test
mode (the "linux-leaks" CI target).

These were picked because we still have a lot of failures in adjacent
areas, and we didn't have much if any coverage of e.g. grep and diff
before this change, we could still whitelist a lot more tests, but
let's stop for now.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>