Added type annotation for "_watched_files".

Author: TobiasRzepka

src/watchdog/observers/read_directory_changes.py

@@ -44,7 +44,7 @@ def __init__(
         super().__init__(event_queue, watch, timeout=timeout, event_filter=event_filter)
         self._lock = threading.Lock()
         self._whandle: HANDLE | None = None
-        self._watched_files = {}
+        self._watched_files: dict[str, str] = {}
 
     def on_thread_start(self) -> None:
         watch_path = self.watch.path