enums: make ARV_PIXEL_FORMAT_CUSTOM_* unsigned integers (#304)
enums: make ARV_PIXEL_FORMAT_CUSTOM_* unsigned integers (#304)

This way the `.gir` file will get generated with the proper type.

See also https://github.com/gtk-rs/gir/issues/850 for more context.
AravisProject/aravis,AravisProject/aravis,AravisProject/aravis,AravisProject/aravis,AravisProject/aravis