Fix importing of certificates

Fixes https://github.com/owncloud/core/issues/19601

settings/controller/certificatecontroller.php

@@ -122,8 +122,9 @@ class CertificateController extends Controller {
 	protected function isCertificateImportAllowed() {
 		$externalStorageEnabled = $this->appManager->isEnabledForUser('files_external');
 		if ($externalStorageEnabled) {
-			$backendService = \OC_Mount_Config::$app->getContainer()->query('OCA\Files_External\Service\BackendService');
-			if ($backendService->getBackendsVisibleFor(\OCA\Files_External\Service\BackendService::VISIBILITY_PERSONAL)) {
+			/** @var \OCA\Files_External\Service\BackendService $backendService */
+			$backendService = \OC_Mount_Config::$app->getContainer()->query('\OCA\Files_External\Service\BackendService');
+			if ($backendService->isUserMountingAllowed()) {
 				return true;
 			}
 		}