The `videosink` refernce in main() is a floating one, so it should not
be unref'ed (the playbin practically takes ownership of it).
This prevents a "gst_object_unref: assertion '((GObject *)
object)->ref_count > 0' failed" at runtime.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6883>
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