feat: easier guards for channelUpdate

[almostSouji]

Please describe the changes this PR makes and why it should be merged:

Below guard fails on channelUpdate client events, however works flawlessly on channelDelete. By adapting the typings to DMChannel | GuildChannel the types are much easier guardable but still encompass all channel types.

if (channel instanceof DMChannel || !channel.isText()) return;

Status and versioning classification:

• I know how to update typings and have done so, or typings don't need updating