Add FIL_RUNOUT_PIN for BIGTREE_SKR_V1.3

See #13267

Marlin/src/pins/pins_BIGTREE_SKR_V1.3.h

@@ -50,6 +50,13 @@
   #define Z_MIN_PROBE_PIN  P1_24
 #endif
 
+//
+// Filament Runout Sensor
+//
+#ifndef FIL_RUNOUT_PIN
+  #define FIL_RUNOUT_PIN   P1_28
+#endif
+
 //
 // Steppers
 //