Make constant for test language in NodaWikidataFetcherTest public, allowing reuse

src/NodaWikidataFetcher.php

@@ -745,7 +745,7 @@ final class NodaWikidataFetcher {
         $languagesToFetch = $wikilinks = [];
         foreach ($checkagainstLanguage as $lang) {
 
-            if (empty($data['labels'][$lang])) {
+            if (empty($data['labels']) || empty($data['labels'][$lang])) {
                 continue;
             }