Fix: Limit readers to excel when testing content

src/TestsExcelDocuments.php

@@ -13,7 +13,7 @@ trait TestsExcelDocuments
     {
         $filename = sys_get_temp_dir() . '/' . str()->uuid()->toString();
         file_put_contents($filename, $content);
-        $spreadsheet = IOFactory::load($filename);
+        $spreadsheet = IOFactory::load($filename, 0, [IOFactory::READER_XLSX]);
         $writer = new Csv($spreadsheet);
         $writer->save($filename);
         $spreadsheet->disconnectWorksheets();