Correctly type display.get_surface() return type

Author: aatle

buildconfig/stubs/pygame/display.pyi

@@ -44,7 +44,7 @@ def set_mode(
     display: int = 0,
     vsync: int = 0,
 ) -> Surface: ...
-def get_surface() -> Surface: ...
+def get_surface() -> Optional[Surface]: ...
 def flip() -> None: ...
 @overload
 def update(