Algorithm change is not handled as a rollover.

>> Otherwise as you say the zone must be removed and re-added.
> 
> If the new policy uses a different algorithm, it seems there is no proper rollover (I changed from 15 to 13 and the new policy fully applies, nothing is left of keys and signatures of the previous algorithm).
>  

 _Originally posted by @bortzmeyer in [#903](https://github.com/NLnetLabs/cascade/issues/903#issuecomment-4978057395)_