fix(GuildChannelManager): allow creating webhooks on forums

[almeidx]

Please describe the changes this PR makes and why it should be merged:
Allows creating webhooks on ForumChannels from the GuildChannelManager

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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1 Ignored Deployment

Name	Status	Preview	Updated
discord-js	⬜️ Ignored (Inspect)		Sep 24, 2022 at 2:29PM (UTC)

[codecov]

Codecov Report

Merging #8661 (99b7c4b) into main (c446a84) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #8661      +/-   ##
==========================================
+ Coverage   86.66%   86.76%   +0.10%     
==========================================
  Files          86       84       -2     
  Lines        8771     8760      -11     
  Branches     1105     1104       -1     
==========================================
  Hits         7601     7601              
+ Misses       1128     1117      -11     
  Partials       42       42              

Flag	Coverage Δ
builders	100.00% <100.00%> (ø)
collection	100.00% <ø> (ø)
proxy	80.46% <ø> (+6.36%)	⬆️
rest	91.99% <ø> (ø)
voice	63.83% <ø> (-0.04%)	⬇️
ws	60.47% <ø> (ø)

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

Impacted Files	Coverage Δ
...ixins/ApplicationCommandOptionChannelTypesMixin.ts	100.00% <100.00%> (ø)
packages/proxy/src/util/util.ts
packages/voice/src/util/util.ts

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