rpc: avoid copying into UniValue

These are simple (and hopefully obviously correct) copies that can be moves
instead.

src/test/script_tests.cpp

@@ -396,7 +396,7 @@ public:
                 wit.push_back(HexStr(scriptWitness.stack[i]));
             }
             wit.push_back(ValueFromAmount(nValue));
-            array.push_back(wit);
+            array.push_back(std::move(wit));
         }
         array.push_back(FormatScript(spendTx.vin[0].scriptSig));
         array.push_back(FormatScript(creditTx->vout[0].scriptPubKey));