t0008: skip trailing space test on Windows

The Windows API does not preserve file names with trailing spaces (and
dots), but rather strips them. Our tools (MSYS bash, git) base the POSIX
emulation on the Windows API. As a consequence, it is impossible for bash
on Windows to allocate a file whose name has trailing spaces, and for git
to stat such a file. Both operate on a file whose name has the spaces
stripped. Skip the test that needs such a file name.

Note that we do not use (another incarnation of) prerequisite FUNNYNAMES.
The reason is that FUNNYNAMES is intended to represent a property of the
file system. But the inability to have trailing spaces in a file name is
a property of the Windows API. The file system (NTFS) does not have this
limitation.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>