Fix VersionedTransaction.Message type hint

`message` property can be either `Message` or `MessageV0`.

python/solders/transaction.pyi

@@ -108,7 +108,7 @@ class VersionedTransaction:
     @signatures.setter
     def signatures(self, signatures: Sequence[Signature]) -> None: ...
     @property
-    def message(self) -> Message: ...
+    def message(self) -> Union[Message, MessageV0]: ...
     @staticmethod
     def populate(
         message: Union[Message, MessageV0], signatures: Sequence[Signature]