fix(examples) remove cast in MP scripts (#2354)

After https://github.com/lvgl/lv_binding_micropython/pull/161 merged, it is no longer needed to cast the result of 'e.get_target()'

Also, additional small fixes to allow CI improvements

examples/widgets/checkbox/lv_example_checkbox_1.py

@@ -1,6 +1,6 @@
 def event_handler(e):
     code = e.get_code()
-    obj = lv.checkbox.__cast__(e.get_target())
+    obj = e.get_target()
     if code == lv.EVENT.VALUE_CHANGED:
         txt = obj.get_text()
         if obj.get_state() & lv.STATE.CHECKED: