main/json-c: upgrade to 0.18
https://github.com/json-c/json-c/compare/json-c-0.17-20230812...json-c-0.18-20240915
https://github.com/json-c/json-c/compare/json-c-0.17-20230812...json-c-0.18-20240915
This could be backported to stable releases, as the 0.17
broke ABI