MDL-81925 filter_mathjaxloader: Fixed replacement of grader or less

Author: chen21590

filter/mathjaxloader/classes/text_filter.php

@@ -246,7 +246,7 @@ protected function insert_span($text, $start, $end) {
      * @return string Returns the input string with HTML tags escaped.
      */
     private function escape_html_tag_wrapper(string $text): string {
-        return preg_replace_callback('/\{([^}]+)\}/', function (array $matches): string {
+        return preg_replace_callback('/\{[^}]*<[^}]+>[^}]*\}/', function (array $matches): string {
             $search = ['<', '>'];
             $replace = ['&lt;', '&gt;'];
             return str_replace($search, $replace, $matches[0]);