Update configuration validation to support root_sass paths defined with keys

Author: evertharmeling

src/DependencyInjection/SymfonycastsSassExtension.php

@@ -61,7 +61,7 @@ public function getConfigTreeBuilder(): TreeBuilder
                         ->end()
                     ->validate()
                         ->ifTrue(static function (array $paths): bool {
-                            if (1 === \count($paths)) {
+                            if (1 === \count($paths) || !\array_is_list($paths)) {
                                 return false;
                             }