Add void return type to collect() method

Needed for Symfony 6.3.

```
 1x: Method "Symfony\Component\HttpKernel\DataCollector\DataCollectorInterface::collect()" might add "void" as a native return type declaration in the future. Do the same in implementation "Http\HttplugBundle\Collector\Collector" now to avoid errors or add an explicit @return annotation to suppress this message.
```

Author: ruudk

src/Collector/Collector.php

@@ -195,7 +195,7 @@ public function getTotalDuration()
     /**
      * {@inheritdoc}
      */
-    public function collect(Request $request, Response $response, $exception = null)
+    public function collect(Request $request, Response $response, $exception = null): void
     {
         // We do not need to collect any data from the Symfony Request and Response
     }