REFACTOR: Migrate Networking tests to Swift Testing

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 89.44%. Comparing base (9ab06cd) to head (33080db). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
Sources/TMDb/Networking/TMDbAPIError.swift	90.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #193 +/- ## ======================================= Coverage 89.43% 89.44% ======================================= Files 203 204 +1 Lines 2820 2860 +40 ======================================= + Hits 2522 2558 +36 - Misses 298 302 +4 ```

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