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

Mark some tests that match "*diff*" 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).

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

t/t4029-diff-trailing-space.sh

@@ -4,6 +4,7 @@
 #
 test_description='diff honors config option, diff.suppressBlankEmpty'
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 cat <<\EOF >expected ||