gitignore: ignore generated test-fake-ssh executable

In "mingw: fix t5601-clone.sh", this developer introduced a new test
executable, test-fake-ssh but forgot to update the .gitignore file
accordingly. Fix that.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitignore

@@ -187,6 +187,7 @@
 /test-dump-cache-tree
 /test-dump-split-index
 /test-dump-untracked-cache
+/test-fake-ssh
 /test-scrap-cache-tree
 /test-genrandom
 /test-hashmap