tests: add missing double quotes to included library paths
Fix inclusion errors which would occur if the $TEST_DIRECTORY had $IFS
whitespace in it.
See
d42bab442d7 (core.fsyncmethod: tests for batch mode, 2022-04-04)
and
a242c150ebb (vimdiff: integrate layout tests in the unit tests
framework ('t' folder), 2022-03-30) for the two relevant commits. Both
were first released with v2.37.0-rc0 (and were also part of v2.37.0).
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>