Rename variable (matrix_user_groupname -> matrix_group_name)

docs/configuring-playbook-bridge-hookshot.md

@@ -127,7 +127,7 @@ aux_file_definitions:
     content: "{{ lookup('file', '/path/to/your-github-private-key.pem') }}"
     mode: '0400'
     owner: "{{ matrix_user_name }}"
-    group: "{{ matrix_user_groupname }}"
+    group: "{{ matrix_group_name }}"
 ```
 
 For more information, see the documentation in the [default configuration of the aux role](https://github.com/mother-of-all-self-hosting/ansible-role-aux/blob/main/defaults/main.yml).