Cannot sign blocks in setup with signblockscript without disabling dynafed

In the elements tutorial covering block signing in a strong federation (i.e. not using generate to create blocks) it uses a 1of1 block signing model and disables dynafed using `con_dyna_deploy_start=9999999999999`. If you don't disable dynafed you get an error:

```
error code: -8
error message:
Signing dynamic blocks requires the witnessScript argument
```

https://elementsproject.org/elements-code-tutorial/block-creation

How can we create blocks that require a set signer/s with dynafed enabled?

This has been like this for a while (version-wise) but tested recently using elements-0.18.1.9