templ is the new one that is being stored and that needs to be ref-sinked,
padtempl is the old one that just needs to be unreffed.
Fixes leaking the old template, and also makes sure that the new template is not
floating which can cause use-after-frees with bindings as they might wrongly
take ownership of a still floating template.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8988>
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