t3700: Skip a test with backslashes in pathspec

The test verifies that glob special characters can be escaped with
backslashes.  In particular, the string fo\[ou\]bar is given to git.

On Windows, this does not work because backslashes are first of all
directory separators, and first thing git does with a pathspec from the
command line is to convert backslashes to forward slashes.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
diff --git a/t/test-lib.sh b/t/test-lib.sh
index f134e73..b4b626e 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -688,9 +688,11 @@
 		builtin pwd -W
 	}
 	# no POSIX permissions
+	# backslashes in pathspec are converted to '/'
 	;;
 *)
 	test_set_prereq POSIXPERM
+	test_set_prereq BSLASHPSPEC
 	;;
 esac