Rename the workflow job and GHCR tags to use a dotnet-prefixed name, and switch GHCR image references from parkervcp to 2sharkystudios. Updates .github/workflows/dotnet.yml to change the job name and tag paths (ghcr.io/.../yolks:dotnet_ -> ghcr.io/.../dotnet:dotnet_), and updates dotnet/9/Dockerfile to use ghcr.io/2sharkystudios/yolks:debian as the base image for consistency.