docs(MessagePayload): Correct return type of resolveFile()

[Jiralite]

Please describe the changes this PR makes and why it should be merged:
Resolves #6604 by correcting the @returns documentation.

Status and versioning classification:

• This PR only includes non-code changes, like changes to documentation, README, etc.

[NotSugden]

perhaps its also an idea to correct the typings

discord.js/typings/index.d.ts

Line 1432 in f57791c

public static resolveFile(fileLike: BufferResolvable | Stream | FileOptions | MessageAttachment): Promise<unknown>;

why was it ever even unknown?

[Jiralite]

I didn't see an interface or type for this actually. files is also typed as unknown[] | null... Isn't the correct type for this HTTPAttachmentData?

discord.js/typings/index.d.ts

Lines 3984 to 3988 in f57791c

	export interface HTTPAttachmentData {
	attachment: string | Buffer | Stream;
	name: string;
	file: Buffer | Stream;
	}

[kyranet]

We can correct the typings in another PR 👍

[Jiralite]

We can correct the typings in another PR 👍

Understood! I have just opened #6608.