[Store] Make Retriever constructor properties readonly

Author: OskarStark

src/store/src/Retriever.php

@@ -22,9 +22,9 @@
 final class Retriever implements RetrieverInterface
 {
     public function __construct(
-        private VectorizerInterface $vectorizer,
-        private StoreInterface $store,
-        private LoggerInterface $logger = new NullLogger(),
+        private readonly VectorizerInterface $vectorizer,
+        private readonly StoreInterface $store,
+        private readonly LoggerInterface $logger = new NullLogger(),
     ) {
     }