[2.0.x] Correct Ender 3 bed size (#12769)

Marlin/src/config/examples/Creality/Ender-3/Configuration.h

 // @section machine
 
 // The size of the print bed
-#define X_BED_SIZE 220
-#define Y_BED_SIZE 220
+#define X_BED_SIZE 235
+#define Y_BED_SIZE 235
 
 // Travel limits (mm) after homing, corresponding to endstop positions.
 #define X_MIN_POS 0