h/t @MariusVanDerWijden for finding and fixing this on devnet 3.
I made the mistake of thinking `PayloadVersion` was correlated with the
`GetPayloadVX` method, but it actually tracks which version of
`PayloadAttributes` were passed to `forkchoiceUpdated`. So far, Prague
does not necessitate a new version of fcu, so there is no need for
`PayloadV4`.
Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>
lightclient