autotest: raise the target airspeed on landing

we were stalling the plane in the final meters of the approach

Tools/autotest/ap1.txt

@@ -3,7 +3,7 @@ QGC WPL 110
 1	0	3	16	0.000000	0.000000	0.000000	0.000000	-35.361553	149.163956	100.000000	1
 2	0	3	16	0.000000	0.000000	0.000000	0.000000	-35.364540	149.162857	100.000000	1
 3	0	3	16	0.000000	0.000000	0.000000	0.000000	-35.361721	149.161835	40.000000	1
-4	0	3	178	0.000000	12.00000	0.000000	0.000000	0.000000	0.000000	12.000000	1
+4	0	3	178	0.000000	12.00000	0.000000	0.000000	0.000000	0.000000	15.000000	1
 5	0	3	16	0.000000	0.000000	0.000000	0.000000	-35.367970	149.164124	25.000000	1
 6	0	3	16	0.000000	0.000000	0.000000	0.000000	-35.366814	149.165878	20.000000	1
 7	0	3	21	0.000000	0.000000	0.000000	0.000000	-35.362911	149.165222	0.000000	1