Explicitly use a shard for caching

See: https://github.com/rails/solid_cache/pull/219

config/cache.yml

@@ -6,10 +6,7 @@ default_options: &default_options
     namespace: <%= Rails.env %>
 
 default_connection: &default_connection
-  connects_to:
-    database:
-      writing: :cache
-      reading: :cache
+  database: :cache
 
 default: &default
   <<: *default_connection

config/initializers/solid_cache.rb

@@ -1,3 +0,0 @@
-Rails.application.configure do
-  config.solid_cache.connects_to = { database: { writing: :cache, reading: :cache } }
-end