idler: adjust distance threshold

Before, the axis limits had an error of 25° so 225° would actually be measured as 250°.

Now after fixing axisUnitToTruncatedUnit to return a more accurate value, the new values are lower. Adjust the distances by 20° to offset previous error.

src/modules/idler.cpp

@@ -64,7 +64,7 @@ void Idler::FinishMove() {
 }
 
 bool Idler::StallGuardAllowed(bool forward) const {
-    const uint8_t checkDistance = forward ? 220 : 200;
+    const uint8_t checkDistance = forward ? 200 : 180;
     return AxisDistance(mm::axisUnitToTruncatedUnit<config::U_deg>(mm::motion.CurPosition<mm::Idler>())) > checkDistance;
 }