[Bug]: Add unit test for upgrade block.

[jgsbennett]

Problem encountered

This system test PR corrects a system test from checking that exactly the current block would be rejected by vega for protocol upgrade proposals. It did that so that it wouldn't be so susceptible to the nodes being fractionality out of sync with what the current block is. However, checking that the current block is rejected would make an excellent unit test, if we don't already have it.

To be clear: Vega behaves correctly at time of writing. This ticket is to check/add a unit test for exactly this case.

Observed behaviour

Upgrade proposal is rejected

Expected behaviour

Upgrade proposal is rejected

Steps to reproduce

1. See test_protocol_upgrade_rejection_invalid_heights

Software version

264e660

Failing test

No response

Jenkins run

No response

Configuration used

No response

Relevant log output

No response