fix typo in host_group_vars config (#75012)

* no need to deprecate, not used directly

  it just documents the use of the setting in loader

changelogs/fragments/host_group_vars_cfg_fix.yaml

@@ -0,0 +1,2 @@
+bugfixes:
+    - host_group_vars vars plugin fixed ini entry, section and key were reversed.

lib/ansible/plugins/vars/host_group_vars.py

@@ -45,8 +45,8 @@ DOCUMENTATION = '''
         env:
           - name: ANSIBLE_YAML_FILENAME_EXT
         ini:
-          - section: yaml_valid_extensions
-            key: defaults
+          - key: yaml_valid_extensions
+            section: defaults
         type: list
     extends_documentation_fragment:
       - vars_plugin_staging