fix yaml error

roles/matrix-base/defaults/main.yml

@@ -142,7 +142,7 @@ matrix_homeserver_url: "https://{{ matrix_server_fqn_matrix }}"
 # Specifies where the homeserver's Client-Server API is on the container network.
 # Where this is depends on whether there's a reverse-proxy in front of the homeserver, which homeserver it is, etc.
 # This likely gets overriden elsewhere.
-matrix_homeserver_container_url=""
+matrix_homeserver_container_url: ""
 
 # Specifies where the homeserver's Federation API is on the container network.
 # Where this is depends on whether there's a reverse-proxy in front of the homeserver, which homeserver it is, etc.