tests: Add metadata test with opus file

This adds a metadata test case for extracting data from an opus test
file. The added file is just converted from test.ogg and the same
metadata fields are used.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
8 jobs for develop in 4 minutes and 35 seconds (queued for 2 seconds)