Do not deprecate header kwarg to Downloader

[codecov[bot]]

Codecov Report

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

Project coverage is 93.40%. Comparing base (b8d4144) to head (bd312c2). Report is 42 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #101 +/- ## ========================================== - Coverage 93.55% 93.40% -0.16% ========================================== Files 5 5 Lines 559 546 -13 ========================================== - Hits 523 510 -13 Misses 36 36 ```

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