Cleanup code so that PHPStan exception is not needed

Our previous way of using `method_exists` for `OCP\Util\addInitScript` was
flagged by PHPStan. Writing the method call a bit differently solved this.
Unfortunately, Scrutinizer is a bit more stupid here and still requires an
inline suppression also with this modified version.

lib/Utility/HtmlUtil.php

@@ -89,7 +89,7 @@ private static function partialContent(string $partialName) {
 	public static function addWebpackScript(string $name) {
 		$manifest = self::getManifest();
 		$hashedName = \substr($manifest["$name.js"], 0, -3); // the extension is cropped from the name in $manifest
-		if (\method_exists('\OCP\Util', 'addInitScript')) {
+		if (\method_exists(\OCP\Util::class, 'addInitScript')) {
 			\OCP\Util::/** @scrutinizer ignore-call */addInitScript('music', '../dist/' . $hashedName);
 		} else {
 			\OCP\Util::addScript('music', '../dist/' . $hashedName);