Fix 404 handling when deleting a manifest (#850)

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.

d25e260d2e (diff-a5e122cd2318f2dc156f373804a59d30355b0c308b9e64f48e0713344fcdba33L164)

Nowadays containerd exposes a public ErrNotFound which we can use
instead.

Fixes #849.

provider/internal/client.go

@@ -24,6 +24,7 @@ import (
 	"os"
 	"strings"
 
+	"github.com/containerd/errdefs"
 	"github.com/distribution/reference"
 	buildx "github.com/docker/buildx/build"
 	"github.com/docker/buildx/builder"
@@ -339,6 +340,9 @@ func (c *cli) ManifestInspect(ctx context.Context, target string) (string, error
 	}
 
 	m, err := rc.ManifestHead(ctx, ref)
+	if errors.Is(err, errs.ErrNotFound) {
+		return "", fmt.Errorf("fetching %q: %w", ref, errdefs.ErrNotFound)
+	}
 	if err != nil {
 		return "", fmt.Errorf("fetching %q: %w", ref, err)
 	}
@@ -359,6 +363,9 @@ func (c *cli) ManifestDelete(ctx context.Context, target string) error {
 		provider.GetLogger(ctx).Warning("this registry does not support deletions")
 		return nil
 	}
+	if errors.Is(err, errs.ErrNotFound) {
+		return nil
+	}
 	if err != nil {
 		return err
 	}