Use older type annotation syntax.

Python 3.10 added the | operator for typing hint alternatives.  Since
this is the only place where that new syntax is used, revert it to use
the Optional type and restore compatibility with Python < 3.10.

canopen/network.py

@@ -33,7 +33,7 @@ class Listener:
 class Network(MutableMapping):
     """Representation of one CAN bus containing one or more nodes."""
 
-    def __init__(self, bus: can.BusABC | None = None):
+    def __init__(self, bus: Optional[can.BusABC] = None):
         """
         :param can.BusABC bus:
             A python-can bus instance to re-use.