use lookup_key in lookup instead of string

wireguard/files/wg.conf

@@ -1,6 +1,6 @@
 {%- macro output_if_set(object, lookup_key, output_key) %}
 {%- if object.get(lookup_key) %}
-{{output_key}} = {{object.get('lookup_key')}}
+{{output_key}} = {{object.get(lookup_key)}}
 {%- endif %}
 {%- endmacro %}
 {%- macro output_list_if_set(object, lookup_key, output_key) %}