Add a Mightyboard pin (#17538)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/pins/mega/pins_MIGHTYBOARD_REVE.h

 #define LED_PIN                               13  // B7
 #define CUTOFF_RESET_PIN                      16  // H1
 #define CUTOFF_TEST_PIN                       17  // H0
+#define CUTOFF_SR_CHECK_PIN                   70  // G4 (TOSC1)
 
 //
 // LCD / Controller