Fix PHP 8.4 "implicit marking parameter as nullable is deprecated"

[ptmkenny]

With a site using the config reader on PHP 8.4, a drush command returns the following:

Deprecated: Platformsh\ConfigReader\Config::__construct(): Implicitly marking parameter $environmentVariables as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/platformsh/config-reader/src/Config.php on line 152
PHP Deprecated:  Platformsh\ConfigReader\Config::getUpstreamRoutes(): Implicitly marking parameter $appName as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/platformsh/config-reader/src/Config.php on line 340

Deprecated: Platformsh\ConfigReader\Config::getUpstreamRoutes(): Implicitly marking parameter $appName as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/platformsh/config-reader/src/Config.php on line 340
PHP Deprecated:  Drupal\key\KeyConfigOverrides::__construct(): Implicitly marking parameter $config_factory as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/web/modules/contrib/key/src/KeyConfigOverrides.php on line 53