tools: add missing <stdint.h> header to codec_config.h
tools: add missing <stdint.h> header to codec_config.h

Without the change libjxl build fails on this week's gcc-13 snapshot as:

    In file included from /build/libjxl/tools/codec_config.cc:6:
    /build/libjxl/tools/codec_config.h:17:31: error: 'uint32_t' was not declared in this scope
       17 | std::string CodecConfigString(uint32_t lib_version);
          |                               ^~~~~~~~
    /build/libjxl/tools/codec_config.h:10:1: note: 'uint32_t' is defined in header '<cstdint>';
      did you forget to '#include <cstdint>'?
        9 | #include <string>
      +++ |+#include <cstdint>
       10 |

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