Add void return type in DoctrineSchemaCompilerPass

Fixes this deprecation on Symfony 6.3:

```
Method "Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface::process()" might add "void" as a native return type declaration in the future. Do the same in implementation "Enqueue\Doctrine\DoctrineSchemaCompilerPass" now to avoid errors or add an explicit @return annotation to suppress this message.
```

Author: ruudk

pkg/enqueue/Doctrine/DoctrineSchemaCompilerPass.php

@@ -11,7 +11,7 @@
 
 class DoctrineSchemaCompilerPass implements CompilerPassInterface
 {
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         if (false === $container->hasDefinition('doctrine')) {
             return;