docs: update misleading Client#guildMemberAvailable event description

[almeidx]

Please describe the changes this PR makes and why it should be merged:
This event is emitted on any guild if an uncached member is updated and the client wasn't instantiated with the GuildMember partial

discord.js/packages/discord.js/src/client/actions/GuildMemberUpdate.js

Lines 21 to 39 in d14d47b

	const member = this.getMember({ user: data.user }, guild);
	if (member) {
	const old = member._update(data);
	/**
	* Emitted whenever a guild member changes - i.e. new role, removed role, nickname.
	* @event Client#guildMemberUpdate
	* @param {GuildMember} oldMember The member before the update
	* @param {GuildMember} newMember The member after the update
	*/
	if (shard.status === Status.Ready && !member.equals(old)) client.emit(Events.GuildMemberUpdate, old, member);
	} else {
	const newMember = guild.members._add(data);
	/**
	* Emitted whenever a member becomes available in a large guild.
	* @event Client#guildMemberAvailable
	* @param {GuildMember} member The member that became available
	*/
	this.client.emit(Events.GuildMemberAvailable, newMember);
	}

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes

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1 Ignored Deployment

Name	Status	Preview	Updated
discord-js	⬜️ Ignored (Inspect)		Sep 15, 2022 at 5:59PM (UTC)

[Jiralite]

Would you mind backporting this?

[codecov]

Codecov Report

Merging #8626 (b330627) into main (4ffdada) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #8626      +/-   ##
==========================================
+ Coverage   86.47%   86.50%   +0.03%     
==========================================
  Files          87       87              
  Lines        8675     8673       -2     
  Branches     1110     1110              
==========================================
+ Hits         7502     7503       +1     
+ Misses       1131     1128       -3     
  Partials       42       42              

Flag	Coverage Δ
builders	100.00% <100.00%> (ø)
collection	100.00% <ø> (ø)
proxy	74.10% <ø> (ø)
rest	91.99% <ø> (ø)
utilities	100.00% <ø> (ø)
voice	63.86% <ø> (ø)
ws	60.47% <ø> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/collection/src/collection.ts	100.00% <ø> (ø)
packages/voice/src/DataStore.ts	98.14% <ø> (ø)
packages/voice/src/networking/Networking.ts	3.18% <ø> (ø)
packages/voice/src/networking/VoiceUDPSocket.ts	90.47% <ø> (ø)
packages/voice/src/networking/VoiceWebSocket.ts	0.00% <ø> (ø)
packages/voice/src/receive/SSRCMap.ts	86.20% <ø> (ø)
packages/voice/src/receive/SpeakingMap.ts	100.00% <ø> (ø)
packages/voice/src/util/Secretbox.ts	33.33% <ø> (ø)
...trategies/context/WorkerContextFetchingStrategy.ts	92.00% <ø> (-0.16%)	⬇️
.../src/strategies/sharding/WorkerShardingStrategy.ts	95.87% <ø> (-0.02%)	⬇️
... and 4 more

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