Fix deprecated on php 8.4

FOS\CKEditorBundle\Command\CKEditorInstallerCommand::block(): Implicitly marking parameter $background as nullable is deprecated, the explicit nullable type must be used instead

FOS\CKEditorBundle\Command\CKEditorInstallerCommand::block(): Implicitly marking parameter $font as nullable is deprecated, the explicit nullable type must be used instead

src/Command/CKEditorInstallerCommand.php

@@ -290,8 +290,8 @@ private function info(string $message, OutputInterface $output): void
     private function block(
         string $message,
         OutputInterface $output,
-        string $background = null,
-        string $font = null
+        ?string $background = null,
+        ?string $font = null
     ): void {
         $options = [];