Fix tentative return type

Author: ondrejmirtes

src/Rules/Methods/OverridingMethodRule.php

@@ -195,7 +195,7 @@ public function processNode(Node $node, Scope $scope): array
 }
 }
 
-if ($reportReturnType) {
+if ($reportReturnType && $prototype->isInternal()->yes()) {
 $reportReturnType = !$this->hasReturnTypeWillChangeAttribute($node->getOriginalNode());
 }
 }