fix css never been loaded

tests/Unit/OCUtilStub.php

@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * Minimal stand-in for the server class OC_Util, which is not part
+ * of the OCP vendor package. Records addStyle() calls for assertions.
+ */
+if (!class_exists(\OC_Util::class, false)) {
+	class OC_Util
+	{
+		/** @var list<array{string, ?string, bool}> */
+		public static array $styles = [];
+
+		public static function addStyle(
+			string $application,
+			?string $file = null,
+			bool $prepend = false
+		): void {
+			self::$styles[] = [$application, $file, $prepend];
+		}
+	}
+}