Update for Ruby >= 3 compatibility

Proc.new without a block used to capture a block passed to a method. This was removed in Ruby 3.

Previously it was a faster way to wrap a block and call it than the &block argument. `yield` is still the quickest way to invoke a passed block and `fetch` requires a block so we can safely call yield w/o checking

Author: agrberg

lib/cacheable/cache_adapters/memory_adapter.rb

@@ -20,7 +20,7 @@ def exist?(key)
       def fetch(key, _options = {})
         return read(key) if exist?(key)
 
-        write(key, Proc.new.call)
+        write(key, yield)
       end
 
       def delete(key)