fix(examples) adjust constant names in Micropython examples (#3532)

Due to spurious enums (https://github.com/lvgl/lv_binding_micropython/issues/199) wrong constant names were generated. Fix these constants.

examples/widgets/btn/lv_example_btn_1.py

@@ -25,7 +25,7 @@ btn2.add_event_cb(event_handler,lv.EVENT.ALL, None)
 
 btn2.align(lv.ALIGN.CENTER,0,40)
 btn2.add_flag(lv.obj.FLAG.CHECKABLE)
-btn2.set_height(lv.SIZE.CONTENT)
+btn2.set_height(lv.SIZE_CONTENT)
 
 label=lv.label(btn2)
 label.set_text("Toggle")

examples/widgets/btn/lv_example_btn_2.py

@@ -51,7 +51,7 @@ btn1 = lv.btn(lv.scr_act())
 btn1.remove_style_all()                          # Remove the style coming from the theme
 btn1.add_style(style, 0)
 btn1.add_style(style_pr, lv.STATE.PRESSED)
-btn1.set_size(lv.SIZE.CONTENT, lv.SIZE.CONTENT)
+btn1.set_size(lv.SIZE_CONTENT, lv.SIZE_CONTENT)
 btn1.center()
 
 label = lv.label(btn1)