Fixed error in example code

An error in the loop function led to the fact that the sensors were never queried.

Author: tk-king

content/hardware/05.nicla/boards/nicla-sense-me/tutorials/cheat-sheet/cheat-sheet.md

@@ -343,7 +343,7 @@ Reading the sensor values:
 
 ```cpp
 void loop(){
-  unsigned long lastCheck= millis();
+  static auto lastCheck = millis();
 
   // Update function should be continuously polled
   BHY2.update();