change(network): Updates minimum protocol version for NU6 on Testnet and Mainnet

[arya2]

Motivation

Zebra should expect its peers to use the NU6 protocol version once NU6 is active.

The relevant ZIP is still in draft status, and the network protocol versions for Testnet and Mainnet may still change.

Part of #8689.

Specifications & References

zcash/zips#878

Solution

• Updates the minimum protocol version for NU6 on Mainnet and Testnet

Related changes:

• Fixes the minimum protocol version for Sapling on custom Testnets and Regtest

Tests

Updates the relevant vectors test.

Follow-up Work

We likely want to update the CURRENT_NETWORK_PROTOCOL_VERSION again before releasing a version of Zebra to deploy NU6 on Mainnet.

PR Author's Checklist

• The PR name will make sense to users.
• The PR provides a CHANGELOG summary.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.

PR Reviewer's Checklist

• The PR Author's checklist is complete.
• The PR resolves the issue.

[oxarbitrage]

LGTM, thanks!