[1.1.x] Limit PID autotune target to maxtemp-15 (#12703)

Marlin/temperature.cpp

@@ -308,6 +308,11 @@ uint8_t Temperature::soft_pwm_amount[HOTENDS];
       return;
     }
 
+    if (target > GHV(BED_MAXTEMP, maxttemp[hotend]) - 15) {
+      SERIAL_ECHOLNPGM(MSG_PID_TEMP_TOO_HIGH);
+      return;
+    }
+
     SERIAL_ECHOLNPGM(MSG_PID_AUTOTUNE_START);
 
     disable_all_heaters(); // switch off all heaters.