leak tests: mark a handful of tests as leak-free

In the topic merged via 5a4f8381b6 (Merge branch
'ab/mark-leak-free-tests', 2021-10-25), a handful of tests in the suite
were marked as leak-free.

Since then, a handful of tests have become leak-free due to changes like

  - 861c56f6f9 (branch: fix a leak in setup_tracking, 2023-06-11), and
  - 866b43e644 (do_read_index(): always mark index as initialized unless
    erroring out, 2023-06-29)

, but weren't updated at the time to mark themselves as such. This leads
to test "failures" when running:

    $ make SANITIZE=leak
    $ make -C t \
        GIT_TEST_PASSING_SANITIZE_LEAK=check \
        GIT_TEST_SANITIZE_LEAK_LOG=true \
        GIT_TEST_OPTS=-vi test

This patch closes those gaps by exporting TEST_PASSES_SANITIZE_LEAK=true
before sourcing t/test-lib.sh on most remaining leak-free tests.

There are a couple of other tests which are similarly leak-free, but not
included in the list of tests touched by this patch. The remaining tests
will be addressed in the subsequent two patches.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5571-pre-push-hook.sh

@@ -4,6 +4,7 @@ test_description='check pre-push hooks'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success 'setup' '

t/t7516-commit-races.sh

@@ -1,6 +1,8 @@
 #!/bin/sh
 
 test_description='git commit races'
+
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success 'race to create orphan commit' '