Add base64 dependency

On modern ruby, base64 moved from MRI Ruby core to a standalone gem.
Without this change, we get this error:

```
lib/puppet_forge/v3/release.rb:5: warning: base64 was loaded from the standard library, but is not part of the default gems starting from Ruby 3.4.0.
You can add base64 to your Gemfile or gemspec to silence this warning.
```

Author: bastelfreak

puppet_forge.gemspec

@@ -22,6 +22,7 @@ Gem::Specification.new do |spec|
 
   spec.add_runtime_dependency "faraday", "~> 2.0"
   spec.add_runtime_dependency "faraday-follow_redirects", "~> 0.3.0"
+  spec.add_runtime_dependency 'base64', '~> 0.2.0'
   spec.add_dependency "semantic_puppet", "~> 1.0"
   spec.add_dependency "minitar",  '~> 1.0', '>= 1.0.2'