[common] Skip TYPE=CLOSED-CAPTIONS lines in m3u8 manifests
According to [1], valid values for TYPE are AUDIO, VIDEO, SUBTITLES
and CLOSED-CAPTIONS. Such a value is found in Anvato master playlists,
though I don't use _extract_m3u8_formats() in the end.
Part of #9522.
[1] https://tools.ietf.org/html/draft-pantos-http-live-streaming-19#section-4.3.4.1