Fix 0007-dispute-freshly-finalized.zndsl failing

[alexggh]

Test started failing after 66051ad which enabled approval coalescing, that was expected to happen because the test required an polkadot_parachain_approval_checking_finality_lag of 0, which can't happen with max_approval_coalesce_count greater than 1 because we always delay the approval for no_show_duration_ticks/2 in case we can coalesce it with other approvals.

So relax a bit the restrictions, since we don't actually care that the lags are 0, but the fact the finalities are progressing and are not stuck.

[sandreim]

@ordian do you have any concerns with this? If so we could turn off coalescing for this test. IIRC we had a good reason to test for a value of 0 here, or maybe I am wrong.

[ordian]

Seems reasonable. I'd probably add some sleep before this check to ensure finality is not lagging after some time.

[ordian]

was this metric also lagging?

[alexggh]

Yes, it was let me figure it why.

[alexggh]

Yeah, that's expected with the way we compute polkadot_parachain_disputes_finality_lag, because DetermineUndisputedChain

polkadot-sdk/polkadot/node/service/src/relay_chain_selection.rs

Line 515 in 809d466

block_descriptions: subchain_block_descriptions,

is called with the list of blocks that are already approved by approval-voting, so when we compute the disputes_finality_lag we already include in it the approval-voting-lag because the subchain number can't be higher than the highest approved block in approval-voting:

polkadot-sdk/polkadot/node/service/src/relay_chain_selection.rs

Line 530 in 809d466

let lag_disputes = initial_leaf_number.saturating_sub(subchain_number);