feat: easier guards for channelUpdate (#5716)

* feat: easier guards for channelUpdate

* typings: more explicit typings for client events involving channels

* docs: event doc consistency regarding channel types

src/client/websocket/handlers/CHANNEL_PINS_UPDATE.js

@@ -14,7 +14,7 @@ module.exports = (client, { d: data }) => {
      * Emitted whenever the pins of a channel are updated. Due to the nature of the WebSocket event,
      * not much information can be provided easily here - you need to manually check the pins yourself.
      * @event Client#channelPinsUpdate
-     * @param {DMChannel|TextChannel} channel The channel that the pins update occurred in
+     * @param {DMChannel|TextChannel|NewsChannel} channel The channel that the pins update occurred in
      * @param {Date} time The time of the pins update
      */
     client.emit(Events.CHANNEL_PINS_UPDATE, channel, time);