gst_pbutils::codec_utils_opus_parse_caps() and other functions should take a `&CapsRef` instead of `&Caps`

See gst-plugins-rs!962 (diffs)

Should also check for &Buffer and other miniobject references, and &Caps in other functions too. This is only correct in places where we know or are not sure if the function keeps a reference around. Functions that just borrow the value shortly should use the Ref type for biggest flexibility.