I found a workaround in How to turn off warnings, 'ruby -w', in 'rake test'? by adding t.warning = false to my Rakefile.

# frozen_string_literal: true
require 'rake/testtask'
require 'bundler/gem_tasks'
Rake::TestTask.new do |t|
  t.libs << 'test'
+  t.warning = false
end
desc 'Run tests'
task default: :test

But that's not ideal since it disable all warnings.