fix app blur

Author: willmcgugan

src/textual/drivers/web_driver.py

@@ -147,7 +147,7 @@ def do_exit() -> None:
         self._enable_bracketed_paste()
         self.flush()
         self._key_thread.start()
-        self._app.post_message(events.AppBlur())
+        self._app.call_later(self._app.post_message, events.AppBlur())
 
     def disable_input(self) -> None:
         """Disable further input."""