The TsMuxStream internal_stream_type field stores the original
'full' stream type (such as Opus), while the stream_type field
stores the value that will actually be written into the MPEG-TS
packets according to the codec mappings. When checking if
input caps are changing stream type, check the original type.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9430>