Avoid incomplete block import pipeline with full verifying import queue (#7050)

## Problem
In the parachain template we use the [fully verifying import queue

](https://github.com/paritytech/polkadot-sdk/blob/3d9eddbe/cumulus/client/consensus/aura/src/equivocation_import_queue.rs#L224-L224)
which does extra equivocation checks.

However, when we import a warp synced block with state, we don't set a
fork choice, leading to an incomplete block import pipeline and error
here:
https://github.com/paritytech/polkadot-sdk/blob/3d9eddbe/substrate/client/service/src/client/client.rs#L488-L488

This renders warp sync useless for chains using this import queue.

## Fix
The fix is to always import a block with state as best block, as we
already do in the normal Aura Verifier.
In a follow up we should also take another look into unifying the usage
of the different import queues.

fixes https://github.com/paritytech/project-mythical/issues/256

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Co-authored-by: command-bot <>