tests: mark tests as passing with SANITIZE=leak

This marks tests that have been leak-free since various recent
commits, but which were not marked us such when the memory leak was
fixed. These were mostly discovered with the "check" mode added in
faececa53f (test-lib: have the "check" mode for SANITIZE=leak
consider leak logs, 2022-07-28).

Commits that fixed the last memory leak in these tests. Per narrowing
down when they started to pass under SANITIZE=leak with "bisect":

- t1022-read-tree-partial-clone.sh:
  7e2619d8ff (list_objects_filter_options: plug leak of filter_spec
  strings, 2022-09-08)

- t4053-diff-no-index.sh: 07a6f94a6d (diff-no-index: release prefixed
  filenames, 2022-09-07)

- t6415-merge-dir-to-symlink.sh: bac92b1f39 (Merge branch
  'js/ort-clean-up-after-failed-merge', 2022-08-08).

- t5554-noop-fetch-negotiator.sh:
  66eede4a37 (prepare_repo_settings(): plug leak of config values,
  2022-09-08)

- t2012-checkout-last.sh, t7504-commit-msg-hook.sh,
  t91{15,46,60}-git-svn-*.sh: The in-flight "pw/rebase-no-reflog-action"
  series, upon which this is based:
  https://lore.kernel.org/git/pull.1405.git.1667575142.gitgitgadget@gmail.com/

Let's mark all of these as passing with
"TEST_PASSES_SANITIZE_LEAK=true", to have it regression tested,
including as part of the "linux-leaks" CI job.

Additionally, let's remove the "!SANITIZE_LEAK" prerequisite from
tests that now pass, these were marked as failing in:

- 77e56d55ba (diff.c: fix a double-free regression in a18d66cefb,
  2022-03-17)
- c4d1d52631 (tests: change some 'test $(git) = "x"' to test_cmp,
  2022-03-07)

These were not spotted with the new "check" mode, but manually, it
doesn't cover these sort of prerequisites. There's few enough that we
shouldn't bother to automate it. They'll be going away sooner than
later.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>

t/t9160-git-svn-preserve-empty-dirs.sh

@@ -9,7 +9,6 @@ This test uses git to clone a Subversion repository that contains empty
 directories, and checks that corresponding directories are created in the
 local Git repository with placeholder files.'
 
-TEST_FAILS_SANITIZE_LEAK=true
 . ./lib-git-svn.sh
 
 GIT_REPO=git-svn-repo