Constrained generator for GOV generates invalid values

[Soupstraw]

I'm getting a conformance failure in #4865 in the GOV rule, because the EnactState from the ConwayGovExecContext is used in the GovState generator. The root of the problem is that we generate some "previous gov action IDs" in the EnactState that is part of the context, but these IDs don't make it to the proposals tree.

I think it'd be a good idea to move ledger-specific conformance code out of cardano-ledger-test before attempting to fix this.

[Soupstraw]

I had accidentally removed some code that overwrites the enactState in the context with valid values.