fix(ThreadChannel): Add forum channel to parent

[Jiralite]

Please describe the changes this PR makes and why it should be merged:
ThreadChannel#parent now documents and types forum channels.

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 2:45PM (UTC)

[codecov]

Codecov Report

Merging #8664 (f830a09) into main (c446a84) will increase coverage by 0.12%.
The diff coverage is 100.00%.

❗ Current head f830a09 differs from pull request most recent head 6d3bb9d. Consider uploading reports for the commit 6d3bb9d to get more accurate results

@@            Coverage Diff             @@
##             main    #8664      +/-   ##
==========================================
+ Coverage   86.66%   86.78%   +0.12%     
==========================================
  Files          86       85       -1     
  Lines        8771     8773       +2     
  Branches     1105     1109       +4     
==========================================
+ Hits         7601     7614      +13     
+ 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)
utilities	100.00% <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/voice/src/util/util.ts
packages/proxy/src/util/util.ts
packages/actions/src/formatTag/formatTag.ts	100.00% <0.00%> (ø)

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