update default backup_methods as proposed by the system anyway

roles/matrix-base/defaults/main.yml

@@ -75,7 +75,7 @@ matrix_client_element_e2ee_backup_required: false
 # Controls which backup methods from ["key", "passphrase"] should be used, both is the default.
 # Setting this to other then empty will update `/.well-known/matrix/client` and tell Element which method to use
 # See: https://github.com/vector-im/element-web/blob/develop/docs/e2ee.md
-matrix_client_element_e2ee_backup_methods: []
+matrix_client_element_e2ee_backup_methods: [ "key", "passphrase" ]
 
 # The Docker network that all services would be put into
 matrix_docker_network: "matrix"