This is needed if the LCEVC enhancement data is part of the video stream as SEI
and the demuxer outputs 'lcevc=false' src caps because LCEVC enhancement data is
not stored as a separate stream in the container.
To clarify, 'lcevc=true' just means that the video buffers have LCEVC metadata
attached. Therefore, it is valid to have a stream with LCEVC enhancement data as
SEI with 'lcevc=false' as long as it is not attached as metadata.
This will be needed once we add support for the demuxer to attach LCEVC metadata
to video buffers if it is stored in a separate track.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9427>
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