Extend SANITIZE=leak checking and declare more tests "currently leak-free".
* ab/leak-check:
CI: use "GIT_TEST_SANITIZE_LEAK_LOG=true" in linux-leaks
upload-pack: fix a memory leak in create_pack_file()
leak tests: mark passing SANITIZE=leak tests as leak-free
leak tests: don't skip some tests under SANITIZE=leak
test-lib: have the "check" mode for SANITIZE=leak consider leak logs
test-lib: add a GIT_TEST_PASSING_SANITIZE_LEAK=check mode
test-lib: simplify by removing test_external
tests: move copy/pasted PERL + Test::More checks to a lib-perl.sh
t/Makefile: don't remove test-results in "clean-except-prove-cache"
test-lib: add a SANITIZE=leak logging mode
t/README: reword the "GIT_TEST_PASSING_SANITIZE_LEAK" description
test-lib: add a --invert-exit-code switch
test-lib: fix GIT_EXIT_OK logic errors, use BAIL_OUT
test-lib: don't set GIT_EXIT_OK before calling test_atexit_handler
test-lib: use $1, not $@ in test_known_broken_{ok,failure}_
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