When pushing several buffers while the pipeline is in NULL state, meaning
that the action are executed "interlaced", previous code was deadlocking.
This new implementation makes it so the override is always on and we
expect all buffers to go through to be associated to a function, which
is a safe assumption.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3052>
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