t0061: fix test for argv[0] with spaces (MINGW only)

t0061: fix test for argv[0] with spaces (MINGW only)

The test was originally designed for the case where user reported
that setting GIT_SSH to a .bat file with spaces in path fails on
Windows: https://github.com/git-for-windows/git/issues/692

The test has two different problems:

1. It succeeds with AND without fix eb7c7863 that addressed user's
   problem. This happens because the core problem was misunderstood,
   leading to conclusion that git is unable to start any programs with
   spaces in path on Win7. But in fact
     a) Bug only affected cmd.exe scripts, such as .bat scripts
     b) Bug only happened when cmd.exe received at least two quoted args
     c) Bug happened on any Windows (verified on Win10).
   Therefore, correct test must involve .bat script and two quoted args.
2. In Visual Studio build, it fails to run, because 'test-fake-ssh.exe'
   is copied away from its dependencies 'libiconv.dll' and 'zlib1.dll'.

Fix both problems by using .bat script instead of 'test-fake-ssh.exe'.
NOTE: With this change, the test now correctly fails without eb7c7863.

Signed-off-by: Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>