Reacting to Cabal/Cabal-syntax split

I ping @RyanGlScott for advice about how to react to the Cabal/Cabal-syntax split.

At the moment patching packages is a bit awkward because

1. We include allow-newer: Cabal in the cabal.project file
2. For HEAD we therefore need to build Setup.hs depending on both Cabal-3.7 and Cabal-syntax-3.7
3. For 9.2 we need to build just depending on Cabal-3.6

I'm unsure how to best express this in a Cabal file. Any advice @RyanGlScott ?