Update splash-test.py

The "splash" property has been deprecated in recent versions of Flet. This patch updates the code to address this issue.

Additionally as per request (#165 (comment))  the bar is now stored in a variable, and we use page.overlay.remove(my_bar) to remove it

python/controls/page/splash-test.py

@@ -1,22 +1,21 @@
 from time import sleep
-
-import flet
+import flet as ft
 from flet import ElevatedButton, ProgressBar
 
-
 def main(page):
     def button_click(e):
-        page.splash = ProgressBar()
+        my_bar = ProgressBar()
+
+        page.overlay.append(my_bar)
         btn.disabled = True
         page.update()
         sleep(3)
-        page.splash = None
+
+        page.overlay.remove(my_bar)
         btn.disabled = False
         page.update()
 
     btn = ElevatedButton("Do some lengthy task!", on_click=button_click)
-
     page.add(btn)
 
-
-flet.app(target=main)
+ft.app(target=main)