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/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)?;