v1.9.0: Symfony 6 Support

Hi!

This release adds support for Symfony 6 and drops old PHP version support.

What's Changed

• Allow Symfony 6.x by @endroid in #301
• • fix deprecations by @garak in #299
• Dropped support for PHP 7.2 and PHP 7.3 by @stephanvierkant in #300

Full Changelog: v1.8.0...v1.9.0