Fixed mypy error for overloaded variable

Author: theeldermillenial

pycardano/cip/cip8.py

@@ -92,15 +92,15 @@ def sign(
     msg.key = cose_key  # attach the key to the message
 
     if isinstance(signing_key, ExtendedSigningKey):
-        message = [
+        _message = [
             msg.phdr_encoded,
             msg.uhdr_encoded,
             msg.payload,
             signing_key.sign(msg._sig_structure),
         ]
 
         encoded = dumps(
-            CBORTag(msg.cbor_tag, message), default=msg._custom_cbor_encoder
+            CBORTag(msg.cbor_tag, _message), default=msg._custom_cbor_encoder
         )
 
     else: