Generate correct URLs for assets for private repos

[dsyme]

We generate

https://raw.githubusercontent.com/github/copilot-chat-aw-test/assets/coffe-scenario-based-eval-daily-score-trending/0ce9fec9dbdd0a6985f35a026f82228f30c996a35bacf0be742024ff9a0eab83.png

which looks like it doesn't work in private repos but generating

https://github.com/github/copilot-chat-aw-test/blob/assets/coffe-scenario-based-eval-daily-score-trending/0ce9fec9dbdd0a6985f35a026f82228f30c996a35bacf0be742024ff9a0eab83.png?raw=true

would work