Use -W:strict_unused_block when running tests on Ruby 3.4+

No changes needed to the code.

Rakefile

@@ -2,7 +2,7 @@ task default: :spec
 
 desc "Run specs"
 task "spec" do
-  sh "#{FileUtils::RUBY} -w spec/all.rb"
+  sh "#{FileUtils::RUBY} -w #{'-W:strict_unused_block' if RUBY_VERSION >= '3.4'} spec/all.rb"
 end
 
 desc "Run specs with coverage"