Fix Duplicator i3 Plus pin diagram (#18862)

Marlin/src/pins/ramps/pins_DUPLICATOR_I3_PLUS.h

  * # Pin | ATMEGA2560 Pin | Arduino #
  * ##################################
  * #  1  | 52 / PG1 (!RD) |    40   #
- * #  2  | 95 / PF2 (A2)  |     2   #
+ * #  2  | 95 / PF2 (A2)  |    56   #
  * #  3  | 54 / PC1 (A9)  |    36   #
  * #  4  | 53 / PC0 (A8)  |    37   #
  * #  5  | 56 / PC3 (A11) |    34   #