Fixed compat with iTunes
Apparently, Itunes doesn't like our URL, so now they look like this:
<enclosure length="4271482" type="audio/mpeg" url="https://node1.funkwhale.test/api/v1/stream/4ce70267-b1bb-42dd-a278-5ed9342431d0.mp3"/>
Cf https://governance.funkwhale.audio/d/s7GTeHwU/podcast-support/22