Fix failing CI with AR 6.1 and Ruby 3.4

Author: n-rodriguez

Appraisals

@@ -7,6 +7,7 @@ appraise "ar-61" do
  # warning: mutex_m was loaded from the standard library, but will no longer be part of the default gems since Ruby 3.4.0.
  # Add mutex_m to your Gemfile or gemspec.
  install_if '-> { Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("3.4.0") }' do
+ gem 'base64'
  gem 'mutex_m'
  end
 end

gemfiles/ar_61.gemfile

@@ -21,6 +21,7 @@ gem "rubocop", ">= 0.69", require: false
 gem "rubocop-discourse", ">= 3", require: false
 
 install_if -> { Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("3.4.0") } do
+ gem "base64"
  gem "mutex_m"
 end