Add and apply Naming/BlockForwarding rubocop rule

This syntax has been added in Ruby 3.1.

Not using a variable name might not be very descriptive, but it's just
as descriptive as using "block" as a variable name. Using just `&` we
get the same amount of information than using `&block`: that we're
passing a block.

We're still using `&action` in `around_action` methods because here we
aren't using a generic name for the variable, so (at least for now) we
aren't running this cop on controllers using `around_action`.

app/controllers/stats_controller.rb

@@ -23,7 +23,7 @@ class StatsController < ApplicationController
 
   private
 
-    def daily_cache(key, &block)
-      Rails.cache.fetch("public_stats/#{Time.current.strftime("%Y-%m-%d")}/#{key}", &block)
+    def daily_cache(key, &)
+      Rails.cache.fetch("public_stats/#{Time.current.strftime("%Y-%m-%d")}/#{key}", &)
     end
 end