df2dcca9a8
Upstream was previously using an internal notFound error, and we were relying on fragile string matching to detect it. This broke when we upgraded to Docker v28. https://github.com/docker/buildx/commit/d25e260d2e3b794c2f0e71aea35a44ca6bdea031#diff-a5e122cd2318f2dc156f373804a59d30355b0c308b9e64f48e0713344fcdba33L164 Nowadays containerd exposes a public ErrNotFound which we can use instead. Fixes #849.