webrtc: fix reading Opus stereo tracks with Chrome (#2043)

[aler9]

Fixes #2043

[codecov]

Codecov Report

Merging #2470 (265051f) into main (c37fd38) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #2470      +/-   ##
==========================================
+ Coverage   61.89%   61.91%   +0.02%     
==========================================
  Files         129      129              
  Lines       14546    14546              
==========================================
+ Hits         9003     9006       +3     
+ Misses       4873     4869       -4     
- Partials      670      671       +1     

Files	Coverage Δ
internal/core/webrtc_manager.go	59.31% <ø> (ø)

... and 5 files with indirect coverage changes

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