MDL-56133 tool_langimport: Changes should be visible after import

Before this change if a language pack was updated by the
\tool_langimport\task\update_langpacks_task scheduled task, changes
would not be available to users until an admin manually cleared the
strings cache.

This change causes the cache to purged when a language pack it update,
this will cause it to rebuild so users will start seeing updates
automatically.

admin/tool/langimport/classes/controller.php

@@ -184,6 +184,8 @@ class controller {
 
         if ($updated) {
             $this->info[] = get_string('langupdatecomplete', 'tool_langimport');
+            // The strings have been changed so we need to purge their cache to ensure users see the changes.
+            get_string_manager()->reset_caches();
         } else {
             $this->info[] = get_string('nolangupdateneeded', 'tool_langimport');
         }