[FIX] bus: fix threads can only be started once

The `ImDispatch` thread uses the `thread.is_alive` method to check
whether or not the thread should be started. The issue is that, this
method will return `False` after the start method has been called, but
before the run method is invoked leading to the RuntimeError: thread
can only be started once.

This commit fixes this issue by suppressing this error in this case.

closes odoo/odoo#103153

Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/bus/models/bus.py

 # -*- coding: utf-8 -*-
+import contextlib
 import datetime
 import json
 import logging
@@ -130,8 +131,9 @@ class ImDispatch(threading.Thread):
         outdated_channels = websocket._channels - channels
         self._clear_outdated_channels(websocket, outdated_channels)
         websocket.subscribe(channels, last)
-        if not self.is_alive():
-            self.start()
+        with contextlib.suppress(RuntimeError):
+            if not self.is_alive():
+                self.start()
 
     def unsubscribe(self, websocket):
         self._clear_outdated_channels(websocket, websocket._channels)