node: annotate Node.upload_config to accept config_xml as bytes

This is what set_config_element actually passes so this fixes a type
error

Author: cdleonard

jenkinsapi/node.py

@@ -379,7 +379,7 @@ def load_config(self) -> None:
         self._config = self.get_config()
         self._get_config_element_tree()
 
-    def upload_config(self, config_xml: str) -> None:
+    def upload_config(self, config_xml: Union[str, bytes]) -> None:
         """
         Uploads config_xml to the config.xml for the node.
         """