automysqlbackp: fix missing permissions for mysqldump

automysqldump passes the --events flag, but without the EVENTS permission a error occures:
> mysqldump: Couldn't execute 'show events': Access denied for user 'automysqlbackup'@'localhost' to database 'mysql' (1044)

nixos/modules/services/backup/automysqlbackup.nix

@@ -112,7 +112,7 @@ in
 
     services.mysql.ensureUsers = optional (config.services.mysql.enable && cfg.config.mysql_dump_host == "localhost") {
       name = user;
-      ensurePermissions = { "*.*" = "SELECT, SHOW VIEW, TRIGGER, LOCK TABLES"; };
+      ensurePermissions = { "*.*" = "SELECT, SHOW VIEW, TRIGGER, LOCK TABLES, EVENT"; };
     };
 
   };