Update async_substrate_interface/protocols.py

Co-authored-by: BD Himes <[email protected]>

Author: immortalizzy

async_substrate_interface/protocols.py

@@ -28,7 +28,7 @@ def crypto_type(self) -> int:
         ...
 
     @property
-    def public_key(self) -> bytes | None:
+    def public_key(self) -> Optional[bytes]:
         ...
 
     @property