Don't create a execution payload with same timestamp as terminal block (#3331)

## Issue Addressed

Resolves #3316 

## Proposed Changes

This PR fixes an issue where lighthouse created a transition block with `block.execution_payload().timestamp == terminal_block.timestamp` if the terminal block was created at the slot boundary.

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -3908,14 +3908,13 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                 ForkName::Base | ForkName::Altair => return Ok(()),
                 _ => {
                     // We are post-bellatrix
-                    if execution_layer
+                    if let Some(payload_attributes) = execution_layer
                         .payload_attributes(next_slot, params.head_root)
                         .await
-                        .is_some()
                     {
                         // We are a proposer, check for terminal_pow_block_hash
                         if let Some(terminal_pow_block_hash) = execution_layer
-                            .get_terminal_pow_block_hash(&self.spec)
+                            .get_terminal_pow_block_hash(&self.spec, payload_attributes.timestamp)
                             .await
                             .map_err(Error::ForkchoiceUpdate)?
                         {

beacon_node/beacon_chain/src/execution_payload.rs

@@ -393,7 +393,7 @@ where
         }
 
         let terminal_pow_block_hash = execution_layer
-            .get_terminal_pow_block_hash(spec)
+            .get_terminal_pow_block_hash(spec, timestamp)
             .await
             .map_err(BlockProductionError::TerminalPoWBlockLookupFailed)?;
 

beacon_node/beacon_chain/src/test_utils.rs

@@ -30,6 +30,7 @@ use rayon::prelude::*;
 use sensitive_url::SensitiveUrl;
 use slog::Logger;
 use slot_clock::TestingSlotClock;
+use state_processing::per_block_processing::compute_timestamp_at_slot;
 use state_processing::{
     state_advance::{complete_state_advance, partial_state_advance},
     StateRootStrategy,
@@ -521,6 +522,11 @@ where
         self.chain.head_beacon_state_cloned()
     }
 
+    pub fn get_timestamp_at_slot(&self) -> u64 {
+        let state = self.get_current_state();
+        compute_timestamp_at_slot(&state, &self.spec).unwrap()
+    }
+
     pub fn get_current_state_and_root(&self) -> (BeaconState<E>, Hash256) {
         let head = self.chain.head_snapshot();
         let state_root = head.beacon_state_root();