fix(codecov): use cobertura

[ckohen]

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

Lcov doesn't work because relative paths and collection isn't uniquely identifiable from file structure.
Cobertura actually seems to be the suggested coverage for ts / js. Checked it does have accurate branch coverage reporting and codecov recognizes the semi relative paths for collection.

Status and versioning classification:

[vercel]

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1 Ignored Deployment

Name	Status	Preview	Updated
discord-js	⬜️ Ignored (Inspect)		Jul 5, 2022 at 10:24AM (UTC)

[codecov]

Codecov Report

Merging #8235 (986013e) into main (eb9ad46) will decrease coverage by 0.65%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #8235      +/-   ##
==========================================
- Coverage   90.27%   89.61%   -0.66%     
==========================================
  Files          78       85       +7     
  Lines        5984     6943     +959     
  Branches      560      991     +431     
==========================================
+ Hits         5402     6222     +820     
- Misses        534      674     +140     
+ Partials       48       47       -1     

Flag	Coverage Δ
builders	97.79% <ø> (-0.11%)	⬇️
collection	87.73% <ø> (∅)
proxy	79.83% <ø> (-0.17%)	⬇️
rest	92.31% <ø> (-0.02%)	⬇️
utilities	50.00% <ø> (+2.63%)	⬆️
voice	64.16% <ø> (+0.25%)	⬆️

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

Impacted Files	Coverage Δ
packages/voice/src/util/Secretbox.ts	33.33% <0.00%> (-2.39%)	⬇️
packages/voice/src/VoiceConnection.ts	81.28% <0.00%> (-1.61%)	⬇️
packages/voice/src/networking/Networking.ts	3.18% <0.00%> (-0.47%)	⬇️
packages/voice/src/util/abortAfter.ts	100.00% <0.00%> (ø)
packages/voice/src/util/demuxProbe.ts	93.33% <0.00%> (ø)
packages/voice/src/joinVoiceChannel.ts	100.00% <0.00%> (ø)
packages/voice/src/util/entersState.ts	100.00% <0.00%> (ø)
packages/voice/src/receive/SpeakingMap.ts	100.00% <0.00%> (ø)
packages/voice/src/audio/AudioPlayerError.ts	0.00% <0.00%> (ø)
packages/voice/src/audio/PlayerSubscription.ts	50.00% <0.00%> (ø)
... and 17 more

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