Fix encointer AURA slot

[ggwpez]

Something wrong, probably here:

try-runtime-cli/core/src/common/empty_block/inherents/providers.rs

Line 126 in 251438f

SlotDuration::from_millis(self.blocktime.as_millis() as u64),

panicked at /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/cumulus-pallet-aura-ext-0.15.0/src/consensus_hook.rs:69:9:
    assertion `left == right` failed: slot number mismatch
      left: Slot(143998834)
     right: Slot(287997668)
thread 'main' panicked at cli/main.rs:326:10:

Looks like it is off by 2x, occurred here: https://github.com/polkadot-fellows/runtimes/actions/runs/11168344347/job/31047391625?pr=463

We do have the --blocktime flag, but i think its not being used here.