Fix unsupported around(:all) RSpec configuration

`around(:all)` is not supported by RSpec and is treated like an
`around(:example)` call.

spec/models/solidus_subscriptions/subscription_spec.rb

@@ -59,7 +59,7 @@
       )
     end
 
-    around(:all) do |e|
+    around do |e|
       successive_skip_limit = SolidusSubscriptions::Config.maximum_successive_skips
       total_skip_limit = SolidusSubscriptions::Config.maximum_total_skips