Transcripts fix support for alternative format types

[SergioEstevao]

📘 Part of: #2185

Fixes #

This PR updates the code so transcript format can have more than one valid mime type that match them.

To test

1. Start the app
2. Open the following podcast: https://pca.st/episode/2cb385e0-e8f2-4b5d-be50-69b203630174
3. Play it and open the full screen player
4. Tap on the Transcript icon
5. Check if the transcript shows correctly

Checklist

• [x] I have considered if this change warrants user-facing release notes and have added them to CHANGELOG.md if necessary.
• [x] I have considered adding unit tests for my changes.
• [x] I have updated (or requested that someone edit) the spreadsheet to reflect any new or changed analytics.

[dangermattic]

	1 Warning
:warning:	This PR is assigned to the milestone 7.73 ❄️. The due date for this milestone has already passed. Please assign it to a milestone with a later deadline or check whether the release for this milestone has already been finished.

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