- Fix add_track to re-use existing transceivers with the same track_id

[jeremy-prater]

I had fixed this previously, but it seems that the sender.id() is not the same as the track.id()

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 61.57%. Comparing base (f9734b7) to head (793959a).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #576 +/- ## ======================================= Coverage 61.57% 61.57% ======================================= Files 532 532 Lines 48940 48940 Branches 12318 12328 +10 ======================================= Hits 30135 30135 + Misses 9590 9589 -1 - Partials 9215 9216 +1 ```

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