RPC/mempool: Skip result type checks for fee_histogram in getmempoolinfo

fee_histogram contains both dynamic-named group objects as well as a numeric total_fees, which the check cannot handle
Long-term, the result is expected to change to avoid this, so just skip it for now

Author: luke-jr

src/rpc/mempool.cpp

@@ -762,7 +762,7 @@ static RPCHelpMan getmempoolinfo()
                 {RPCResult::Type::NUM, "incrementalrelayfee", "minimum fee rate increment for mempool limiting or replacement in " + CURRENCY_UNIT + "/kvB"},
                 {RPCResult::Type::NUM, "unbroadcastcount", "Current number of transactions that haven't passed initial broadcast yet"},
                 {RPCResult::Type::BOOL, "fullrbf", "True if the mempool accepts RBF without replaceability signaling inspection"},
-                {RPCResult::Type::OBJ, "fee_histogram", /*optional=*/true, "",
+                {RPCResult::Type::OBJ_DYN, "fee_histogram", /*optional=*/true, "",
                     {
                         {RPCResult::Type::OBJ, "<fee_rate_group>", "Fee rate group named by its lower bound (in " + CURRENCY_ATOM + "/vB), identical to the \"from_feerate\" field below",
                             {