lib-patch-mode.sh: Fix permission

In the same sprit as 4848509a (Fix permissions on test scripts,
2007-04-13), t/lib-patch-mode.sh should not be executable.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/lib-patch-mode.sh

+: included from t2016 and others
+
 . ./test-lib.sh
 
 set_state () {