t5601-99: Enable colliding file detection for MINGW
Commit
b878579ae7 (clone: report duplicate entries on case-insensitive
filesystems - 2018-08-17) adds a warning to user when cloning a repo
with case-sensitive file names on a case-insensitive file system.
This test has never been enabled for MINGW.
It had been working since day 1, but I forget to report that to the
author.
Enable it after a re-test.
Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>