Add traces test dependency

[ioquatix]

Summary

• Add traces to Falcon's test dependencies now that async-http no longer provides it transitively.
• Adjust Falcon middleware trace provider tests to execute the traced block directly while checking emitted trace arguments.
• Add an Unreleased note.

Testing

• bundle exec sus test/traces/provider/falcon/middleware.rb
• bundle exec rubocop gems.rb test/traces/provider/falcon/middleware.rb