Add missing rails-7-1 to docker-compose.yml

The Dockerfile was added in #199
but not added to this file, so I don't think it is actually used.

Author: jamiecobbett

meta_request/docker-compose.yml

@@ -21,3 +21,7 @@ services:
     build:
       context: .
       dockerfile: Dockerfile-rails-7.0
+  test-rails-7.1:
+    build:
+      context: .
+      dockerfile: Dockerfile-rails-7.1