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

No changes needed to the code.

Rakefile

@@ -50,7 +50,7 @@ end
 
 desc "Run specs"
 task :spec do
-  sh "#{FileUtils::RUBY} #{'-w' if RUBY_VERSION >= '3'} spec/all.rb"
+  sh "#{FileUtils::RUBY} #{'-w' if RUBY_VERSION >= '3'} #{'-W:strict_unused_block' if RUBY_VERSION >= '3.4'} spec/all.rb"
 end
 task :default => :spec