src/network/protocols/ranking.hpp: add missing <stdint.h> include

[trofi]

Without the chnage the build fails on upcoming gcc-15 as:

/build/source/src/network/protocols/ranking.hpp:31:5: error: 'uint32_t' does not name a type
   31 |     uint32_t online_id;
      |     ^~~~~~~~

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[kimden]

#5310 added <cstdint> too, I suppose at this point STK should just migrate github actions to gcc 15