add account id to batch serialization

src/libxrpl/protocol/STTx.cpp

@@ -417,6 +417,7 @@ STTx::checkBatchSingleSign(STObject const& batchSigner) const
 {
     Serializer msg;
     serializeBatch(msg, getFlags(), getBatchTransactionIDs());
+    finishMultiSigningData(batchSigner.getAccountID(sfAccount), msg);
     return singleSignHelper(batchSigner, msg.slice());
 }
 

src/test/app/Batch_test.cpp

@@ -550,6 +550,7 @@ class Batch_test : public beast::unit_test::suite
 
             Serializer msg;
             serializeBatch(msg, tfAllOrNothing, jt.stx->getBatchTransactionIDs());
+            finishMultiSigningData(bob.id(), msg);
             auto const sig = xrpl::sign(bob.pk(), bob.sk(), msg.slice());
             jt.jv[sfBatchSigners.jsonName][0u][sfBatchSigner.jsonName][sfAccount.jsonName] =
                 bob.human();

src/test/jtx/impl/batch.cpp

@@ -74,6 +74,7 @@ sig::operator()(Env& env, JTx& jt) const
 
         Serializer msg;
         serializeBatch(msg, stx.getFlags(), stx.getBatchTransactionIDs());
+        finishMultiSigningData(e.acct.id(), msg);
         auto const sig = xrpl::sign(*publicKeyType(e.sig.pk().slice()), e.sig.sk(), msg.slice());
         jo[sfTxnSignature.getJsonName()] = strHex(Slice{sig.data(), sig.size()});
     }