types(Collection): make fn return type unknown

[ImRodry]

Please describe the changes this PR makes and why it should be merged:

This PR changes the type signature for all function parameters in the Collection class by making their return types unknown. This brings the types in line with the TypeScript lib types for the corresponding array methods. Since we're simply checking for truthiness in an if statement, the return type can be converted to a boolean automatically and doesn't need to be provided as one necessarily

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 25, 2022 at 11:34AM (UTC)

[codecov]

Codecov Report

Merging #8676 (2d6cedd) into main (c446a84) will increase coverage by 0.12%.
The diff coverage is 100.00%.

❗ Current head 2d6cedd differs from pull request most recent head 96b90a2. Consider uploading reports for the commit 96b90a2 to get more accurate results

@@            Coverage Diff             @@
##             main    #8676      +/-   ##
==========================================
+ 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% <100.00%> (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)

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Impacted Files	Coverage Δ
...ixins/ApplicationCommandOptionChannelTypesMixin.ts	100.00% <100.00%> (ø)
packages/collection/src/collection.ts	100.00% <100.00%> (ø)
packages/proxy/src/util/util.ts
packages/voice/src/util/util.ts
packages/actions/src/formatTag/formatTag.ts	100.00% <0.00%> (ø)

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