recognize OGG as an audio format

[earl-warren]

• OGG is officially an container format and is therefor classified as application/ogg in RFC3534. While audio/ogg exists, as defined in RFC5334, it doesn't have a different magic number and thus purely informative, it can only be determined by parsing the file and checking if it only contains audio data.
• A quick search on Wikimedia Commons yields that the OGG container is by far more used for audio than for video, so it's safe to classify this as audio, as OGG files that only contain video would now falsy be classified as an audio file (previously it would've shown just a link to the 'View Raw' link).
• Added unit tests.
• Resolves https://codeberg.org/forgejo/forgejo/issues/1091

(cherry picked from commit f5fa1a245236527dd41af4e71b5486c1a39e898a)

[wxiaoguang]

This assumption is not right

https://en.wikipedia.org/wiki/Ogg

The Ogg container format can multiplex a number of independent streams for audio, video, text (such as subtitles), and metadata.

[lunny]

This assumption is not right

https://en.wikipedia.org/wiki/Ogg

The Ogg container format can multiplex a number of independent streams for audio, video, text (such as subtitles), and metadata.

The extension name is .ogx for application/ogg? Maybe RFC 3534 has been obsoleted by RFC 5334 so we don't need to support application/ogg

In May 2003, two Internet RFCs were published relating to the format. The Ogg bitstream was defined in RFC 3533 (which is classified as 'informative') and its Internet content type (application/ogg) in RFC 3534 (which is, as of 2006, a proposed standard protocol). In September 2008, RFC 3534 was obsoleted by RFC 5334, which added content types video/ogg, audio/ogg and filename extensions .ogx, .ogv, .oga, .spx.

[wxiaoguang]

-> Detect ogg mime-type as audio or video #26494