fix: update firebase/php-jwt version to ^7.0 (sec issue) - #48

Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpunit/phpunit ^9.0 -> satisfiable by phpunit/phpunit[9.6.33, 9.6.34]. - phpunit/phpunit[9.6.33, ..., 9.6.34] require doctrine/instantiator ^1.5.0 || ^2 -> found doctrine/instantiator[1.5.0, 2.0.0, 2.1.0] but it conflicts with your root composer.json require (1.4.0).