✨ Add an example of screen callbacks working fine

For Textualize/textual#4656

screen_callback.py

@@ -0,0 +1,38 @@
+"""Evidence that screen callbacks are still working.
+
+For a reply to https://github.com/Textualize/textual/issues/4656.
+"""
+
+from textual import on
+from textual.app import App, ComposeResult
+from textual.screen import Screen
+from textual.widgets import Button
+
+
+class Test(Screen[str]):
+    def compose(self) -> ComposeResult:
+        yield Button("Yes", id="Yes")
+        yield Button("No", id="No")
+
+    @on(Button.Pressed)
+    def test_the_callback(self, event: Button.Pressed) -> None:
+        assert event.button.id is not None
+        self.dismiss(event.button.id)
+
+
+class ScreenCallbackTest(App[None]):
+    def compose(self) -> ComposeResult:
+        yield Button("Test")
+
+    @on(Button.Pressed)
+    def test_screen_callback(self) -> None:
+        def show_result(result: str) -> None:
+            self.notify(result)
+
+        self.push_screen(Test(), callback=show_result)
+
+
+if __name__ == "__main__":
+    ScreenCallbackTest().run()
+
+### screen_callback.py ends here