chore(deps): sync composer.lock with require-dev additions

wp-phpunit, yoast/phpunit-polyfills and symfony/yaml were added to
composer.json without regenerating the lock; CI installs from lock and
aborts on the drift.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011L6cwv6s34nJew65PC7jKN

Author: titustangible