Add (correct) missing pin definitions for Y2

I tested this and it works.

Marlin/pins.h

     #define Z_MIN_PIN          18
     #define Z_MAX_PIN          -1
 
+    #define Y2_STEP_PIN        36
+    #define Y2_DIR_PIN         34
+    #define Y2_ENABLE_PIN      30
+
     #define Z2_STEP_PIN        36
     #define Z2_DIR_PIN         34
     #define Z2_ENABLE_PIN      30
     #define Z_MIN_PIN          18
     #define Z_MAX_PIN          19
 
+    #define Y2_STEP_PIN        36
+    #define Y2_DIR_PIN         34
+    #define Y2_ENABLE_PIN      30
+
     #define Z2_STEP_PIN        36
     #define Z2_DIR_PIN         34
     #define Z2_ENABLE_PIN      30