community/libgdiplus: move from testing

microsoft docs handily tell people to do

apk add libgdiplus --repository https://dl-3.alpinelinux.org/alpine/edge/testing/
https://archive.vn/https://learn.microsoft.com/en-us/dotnet/core/install/linux-alpine

so technically, this is a breaking change for that. it's also annoying they recommend it at all

move this to community to fix this for stable