Fix: implement getMixHashOrPrevRandao to return the acutal value in the block header (#3839)

Signed-off-by: Fabio Di Fabio <fabio.difabio@consensys.net>

CHANGELOG.md

@@ -9,6 +9,7 @@
 
 ### Bug Fixes
 - Stop the BlockPropagationManager when it receives the TTD reached event [#3809](https://github.com/hyperledger/besu/pull/3809)
+- Correct getMixHashOrPrevRandao to return the value present in the block header [#3839](https://github.com/hyperledger/besu/pull/3839)
 
 ## 22.4.0
 

ethereum/core/src/main/java/org/hyperledger/besu/ethereum/core/ProcessableBlockHeader.java

@@ -140,6 +140,16 @@ public class ProcessableBlockHeader implements BlockValues {
     return Optional.ofNullable(baseFee);
   }
 
+  /**
+   * Returns the mixHash before merge, and the prevRandao value after
+   *
+   * @return the mixHash before merge, and the prevRandao value after
+   */
+  @Override
+  public Bytes32 getMixHashOrPrevRandao() {
+    return mixHashOrPrevRandao;
+  }
+
   /**
    * Returns the prevRandao of the block.
    *