dir: fix directory-matching bug

dir: fix directory-matching bug

This reverts the change from ed49584 (dir: fix pattern matching on dirs,
2021-09-24), which claimed to fix a directory-matching problem without a
test case. It turns out to _create_ a bug, but it is a bit subtle.

The bug would have been revealed by the first of two tests being added to
t0008-ignores.sh. The first uses a pattern "/git/" inside the a/.gitignores
file, which matches against 'a/git/foo' but not 'a/git-foo/bar'. This test
would fail before the revert.

The second test shows what happens if the test instead uses a pattern "git/"
and this test passes both before and after the revert.

The difference in these two cases are due to how
last_matching_pattern_from_list() checks patterns both if they have the
PATTERN_FLAG_MUSTBEDIR and PATTERN_FLAG_NODIR flags. In the case of "git/",
the PATTERN_FLAG_NODIR is also provided, making the change in behavior in
match_pathname() not affect the end result of
last_matching_pattern_from_list().

Reported-by: Glen Choo <chooglen@google.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>