add libgmpxx and libffi to runtime dependencies
Those two libraries are needed by octez-sc-rollup-node-alpha
according to this failing job: https://gitlab.com/tezos/tezos/-/jobs/3387190127
Those two libraries are needed by octez-sc-rollup-node-alpha
according to this failing job: https://gitlab.com/tezos/tezos/-/jobs/3387190127