Skip importing validate_config task when Synapse is disabled

roles/matrix-synapse/tasks/main.yml

@@ -3,7 +3,7 @@
     - always
 
 - import_tasks: "{{ role_path }}/tasks/validate_config.yml"
-  when: run_setup|bool
+  when: run_setup|bool and matrix_synapse_enabled|bool
   tags:
     - setup-all
     - setup-synapse