wildmatch test: mark test as EXPENSIVE_ON_WINDOWS

wildmatch test: mark test as EXPENSIVE_ON_WINDOWS

Mark the newly added test which creates test files on-disk as
EXPENSIVE_ON_WINDOWS. According to [1] it takes almost ten minutes to
run this test file on Windows after this recent change, but just a few
seconds on Linux as noted in my [2].

This could be done faster by exiting earlier, however by using this
pattern we'll emit "skip" lines for each skipped test, making it clear
we're not running a lot of them in the TAP output, at the cost of some
overhead.

1. nycvar.QRO.7.76.6.1801061337020.1337@wbunaarf-fpuvaqryva.tvgsbejvaqbjf.bet
   (https://public-inbox.org/git/nycvar.QRO.7.76.6.1801061337020.1337@wbunaarf-fpuvaqryva.tvgsbejvaqbjf.bet/)

2. 87mv1raz9p.fsf@evledraar.gmail.com
   (https://public-inbox.org/git/87mv1raz9p.fsf@evledraar.gmail.com/)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>