Add .alac to accepted file extensions

[audiodude]

The file extension .alac was added in a recent Bandcamp version we upgraded to, but wasn't included in the allowed file list.

[codecov-commenter]

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Codecov Report

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

Project coverage is 95.79%. Comparing base (25ce157) to head (ba8b297).

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #47 +/- ## ======================================= Coverage 95.79% 95.79% ======================================= Files 30 30 Lines 2021 2021 ======================================= Hits 1936 1936 Misses 85 85 ```

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