Create a state containing post-NU5 blocks

[upbqdn]

Address https://github.com/ZcashFoundation/zebra/blob/824e5200e22438c322914cd776f0b89808a98e97/zebra-rpc/src/methods/tests/snapshot.rs#L72-L80

Being able to create a state containing blocks for which we could activate NU5 is beneficial for tests, see: #8535.

Blocks #8535.

[mpguerra]

@ZcashFoundation/zebra-team Is this still relevant?

[upbqdn]

Yes, it is. We don't have a test chain with post-NU5 blocks.