leak tests: mark all checkout-index tests as passing with SANITIZE=leak

leak tests: mark all checkout-index tests as passing with SANITIZE=leak

Mark some tests that match "*{checkout,switch}*" 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).

Unfortunately almost all of those tests fail when compiled with
SANITIZE=leak, these only pass because they run "checkout-index", not
the main "checkout" command.

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