set should_override_builder to false by default

crates/payload/builder/src/payload.rs

@@ -65,6 +65,7 @@ impl BuiltPayload {
     pub fn into_v2_payload(self) -> ExecutionPayloadEnvelope {
         let mut envelope: ExecutionPayloadEnvelope = self.into();
         envelope.blobs_bundle = None;
+        envelope.should_override_builder = None;
         envelope
     }
 
@@ -93,7 +94,15 @@ impl From<BuiltPayload> for ExecutionPayloadEnvelope {
         ExecutionPayloadEnvelope {
             block_value: fees,
             payload: block.into(),
-            should_override_builder: None,
+            // From the engine API spec:
+            //
+            // > Client software **MAY** use any heuristics to decide whether to set
+            // `shouldOverrideBuilder` flag or not. If client software does not implement any
+            // heuristic this flag **SHOULD** be set to `false`.
+            //
+            // Spec:
+            // <https://github.com/ethereum/execution-apis/blob/fe8e13c288c592ec154ce25c534e26cb7ce0530d/src/engine/cancun.md#specification-2>
+            should_override_builder: Some(false),
             blobs_bundle: Some(sidecars.into()),
         }
     }