Merge pull request #17078 from nextcloud/fix/default_csp_404

set default CSP on NotFoundResponse

lib/public/AppFramework/Http/NotFoundResponse.php

@@ -37,6 +37,7 @@ class NotFoundResponse extends Response {
 	public function __construct() {
 		parent::__construct();
 
+		$this->setContentSecurityPolicy(new ContentSecurityPolicy());
 		$this->setStatus(404);
 	}