Fix manual fan check menu

lcd_encoder was not being updated
we need to call manage_inactivity

Tested on MK3S+

Change in memory:
Flash: +6 bytes
SRAM: 0 bytes

Firmware/ultralcd.cpp

@@ -6939,6 +6939,7 @@ static bool lcd_selftest_manual_fan_check(int _fan, bool check_opposite,
 
 
 		manage_heater();
+		manage_inactivity(true);
 		_delay(100);
 
 	} while (!lcd_clicked());