MDL-71899 performance: Improve course image caching

Changed to use get_course() instead of get_fast_modinfo() for better performance

course/classes/cache/course_image.php

@@ -56,7 +56,8 @@ public static function get_instance_for_cache(cache_definition $definition): cou
      * @return string|bool Returns course image url as a string or false if the image is not exist
      */
     public function load_for_cache($key) {
-        $course = get_fast_modinfo($key)->get_course();
+        // We should use get_course() instead of get_fast_modinfo() for better performance.
+        $course = get_course($key);
         return $this->get_image_url_from_overview_files($course);
     }