[sniper only] CI: Use a more appropriate Docker image
Some of our dependencies pull in packages that are unique to Debian 11 or unique to sniper, so we can't use a Debian-10-based image.
I'll probably merge this unreviewed if successful.
Some of our dependencies pull in packages that are unique to Debian 11 or unique to sniper, so we can't use a Debian-10-based image.
I'll probably merge this unreviewed if successful.