Transaction builder must not set consensus branch ID for V4 transactions.

src/transaction_builder.cpp

@@ -522,6 +522,7 @@ void TransactionBuilder::CheckOrSetUsingSprout()
         auto txVersionInfo = CurrentTxVersionInfo(consensusParams, nHeight, usingSprout.value());
         mtx.nVersionGroupId = txVersionInfo.nVersionGroupId;
         mtx.nVersion        = txVersionInfo.nVersion;
+        mtx.nConsensusBranchId = std::nullopt;
     }
 }