scripted-diff: Use UniValue::find_value method

-BEGIN VERIFY SCRIPT-
 sed --regexp-extended -i 's/find_value\(([^ ,]+), /\1.find_value(/g' $(git grep -l find_value)
-END VERIFY SCRIPT-

src/rpc/mempool.cpp

@@ -638,7 +638,7 @@ static RPCHelpMan gettxspendingprevout()
                                 }, /*fAllowNull=*/false, /*fStrict=*/true);
 
                 const uint256 txid(ParseHashO(o, "txid"));
-                const int nOutput{find_value(o, "vout").getInt<int>()};
+                const int nOutput{o.find_value("vout").getInt<int>()};
                 if (nOutput < 0) {
                     throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid parameter, vout cannot be negative");
                 }