leak tests: mark t3321-notes-stripspace.sh as leak-free

leak tests: mark t3321-notes-stripspace.sh as leak-free

This test was leak-free when t3321 was originally introduced, but never
marked as such:

    $ rev="$(git log --format='%H' --reverse -1 HEAD^ -- t/t3321-notes-stripspace.sh)"
    $ git checkout $rev

    $ make SANITIZE=leak
    [...]

    $ make -C t GIT_TEST_PASSING_SANITIZE_LEAK=check GIT_TEST_OPTS=--immediate t3321-notes-stripspace.sh
    [...]
    # passed all 27 test(s)
    1..27
    # faking up non-zero exit with --invert-exit-code
    make: *** [Makefile:66: t3321-notes-stripspace.sh] Error 1
    make: Leaving directory '/home/ttaylorr/src/git/t'

Mark this test as leak-free accordingly.

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