Ruby 3.3: warning related to base64 missing in the gemspec

[tagliala]

~/.rvm/gems/ruby-3.3.0/gems/dalli-3.2.6/lib/dalli/protocol/meta/key_regularizer.rb:3: warning: base64 was loaded from the standard library, but will no longer be part of the default gems since Ruby 3.4.0. Add base64 to your Gemfile or gemspec. Also contact author of dalli-3.2.6 to add base64 into its gemspec.

Going to submit a PR