fixed syntax

roles/matrix-synapse/defaults/main.yml

@@ -595,7 +595,7 @@ matrix_synapse_media_storage_provider_s3_secret_access_key: ""
 matrix_synapse_media_storage_provider_s3_storage_class: "STANDARD"
 matrix_synapse_media_storage_provider_s3_threadpool_size: "20"
 
-matrix_synapse_media_storage_provider_s3_config: {{ matrix_synapse_media_storage_provider_s3_config_yaml|from_yaml }}
+matrix_synapse_media_storage_provider_s3_config: "{{ matrix_synapse_media_storage_provider_s3_config_yaml|from_yaml }}"
 matrix_synapse_media_storage_provider_s3_config_yaml: |
   store_local: {{ matrix_synapse_s3_media_store_on_s3 }}
   store_remote: {{ matrix_synapse_s3_media_store_on_local_filesystem }}