fix(GuildMemberManager): Fix data type check for add() method

[Jiralite]

Please describe the changes this PR makes and why it should be merged:
Resolves #10337 by checking for an ArrayBuffer instead.

I was also able to reproduce an empty array buffer response instead of a Uint8Array. The trace verifies this:

Trace: 
    at parseResponse (/Users/jiralite/Documents/code/GitHub/discordjs/discord.js/packages/rest/src/lib/utils/utils.ts:59:10)
    at _REST.request (/Users/jiralite/Documents/code/GitHub/discordjs/discord.js/packages/rest/src/lib/REST.ts:211:10)
    at processTicksAndRejections (node:internal/process/task_queues:95:5)
    at GuildMemberManager.add (/Users/jiralite/Documents/code/GitHub/discordjs/discord.js/packages/discord.js/src/managers/GuildMemberManager.js:130:18)
    at Client.<anonymous> (file:///Users/jiralite/Documents/code/GitHub/Soulobby/Soulobby/test.ts:16:14)

discord.js/packages/rest/src/lib/utils/utils.ts

Lines 54 to 60 in 8538429

	export async function parseResponse(res: ResponseLike): Promise<unknown> {
	if (res.headers.get('Content-Type')?.startsWith('application/json')) {
	return res.json();
	}
	return res.arrayBuffer();
	}

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

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