MDL-59709 mod_assign: Export to portfolio button not working

Changed the button to a text link

mod/assign/locallib.php

@@ -3181,7 +3181,7 @@ class assign {
             } else {
                 $button->set_formats(PORTFOLIO_FORMAT_PLAINHTML);
             }
-            $result .= $button->to_html();
+            $result .= $button->to_html(PORTFOLIO_ADD_TEXT_LINK);
         }
         return $result;
     }