Add return type unions to private/internal/final/test methods

Author: nicolas-grekas

Tests/Loader/FileLocatorStub.php

@@ -6,7 +6,7 @@
 
 class FileLocatorStub implements FileLocatorInterface
 {
-    public function locate(string $name, string $currentPath = null, bool $first = true)
+    public function locate(string $name, string $currentPath = null, bool $first = true): string|array
     {
         if (0 === strpos($name, 'http')) {
             return $name;