Fix netconf_config backup string issue (ansible#56175)

*  Convert the ElementTree object to string
   before dumping the configuration in file.

lib/ansible/modules/network/netconf/netconf_config.py

@@ -252,6 +252,11 @@
 from ansible.module_utils.connection import Connection, ConnectionError
 from ansible.module_utils.network.netconf.netconf import get_capabilities, get_config, sanitize_xml
 
+try:
+    from lxml.etree import tostring
+except ImportError:
+    from xml.etree.ElementTree import tostring
+
 
 def main():
     """ main entry point for module execution
@@ -365,7 +370,7 @@ def main():
     try:
         if module.params['backup']:
             response = get_config(module, target, lock=execute_lock)
-            before = to_text(response, errors='surrogate_then_replace').strip()
+            before = to_text(tostring(response), errors='surrogate_then_replace').strip()
             result['__backup__'] = before.strip()
         if validate:
             conn.validate(target)