Gloas fix proposer preferences gossip verification (#9337)

Ensure we are using the correct state when validating proposer preferences over gossip. Previously we were only using the head state. At epoch boundaries the head state could be at `current_epoch - 1`. Peers submitting proposer preferences for `current_epoch + 1` would be penalized because our head states lookahead did not have proposer duties for `current_epoch + 1`


  


Co-Authored-By: Eitan Seri-Levi <eserilev@ucsc.edu>

beacon_node/http_api/tests/tests.rs

@@ -2924,8 +2924,16 @@ impl ApiTester {
             .get(lookahead_index)
             .expect("slot index should be in lookahead") as usize;
 
+        let dependent_root = head_state
+            .proposer_shuffling_decision_root_at_epoch(
+                proposal_slot.epoch(E::slots_per_epoch()),
+                head.beacon_block_root,
+                &self.chain.spec,
+            )
+            .expect("should compute proposer shuffling decision root");
+
         let preferences = ProposerPreferences {
-            dependent_root: Hash256::ZERO,
+            dependent_root,
             proposal_slot,
             validator_index: validator_index as u64,
             fee_recipient: Address::repeat_byte(0xaa),