Fix syntax breakage

Regression since 96afbbb5af

roles/matrix-nginx-proxy/tasks/setup_nginx_proxy.yml

@@ -38,7 +38,7 @@
   when: "matrix_nginx_proxy_proxy_synapse_metrics_basic_auth_enabled and matrix_nginx_proxy_proxy_synapse_metrics"
 
 - name: Ensure matrix-synapse-metrics-htpasswd is mounted into the matrix-nginx-proxy container
-  - set_fact:
+  set_fact:
     matrix_nginx_proxy_container_additional_volumes: >
       {{ matrix_nginx_proxy_container_additional_volumes }}
       +