prevent steppers from turning off during manual probes

Marlin/src/feature/bedlevel/ubl/ubl_G29.cpp

       wait_for_release();
       while (!is_lcd_clicked()) {
         idle();
+        gcode.refresh_cmd_timeout();
         if (encoder_diff) {
           do_blocking_move_to_z(current_position[Z_AXIS] + float(encoder_diff) * multiplier);
           encoder_diff = 0;