Fix flaky test in `dispute-coordinator` (#6524)

https://github.com/paritytech/polkadot/pull/6494 updates disputes
participation priority on Active Leaves update. This operation might
trigger participation in some cases and as a result some of the message
ordering is not as nice as it used to be.

As a side effect of this `resume_dispute_without_local_statement` was
failing occasionally. The solution is not to expect that `BlockNumber`,
`CandidateEvents`, `FetchOnChainVotes` and `Ancestors` messages are
executed after `FinalizedBlockNumber` and in any specific order.

This should be okay as the code is in helper function and doesn't affect
the actual test behaviour.

Fixes https://github.com/paritytech/polkadot/issues/6514