vendor: update buildkit to master@2d91ddcceedc

Signed-off-by: Justin Chadwell <me@jedevc.com>
(cherry picked from commit 0a7f96cbfb)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/github.com/moby/buildkit/util/testutil/integration/containerd.go

@@ -230,6 +230,10 @@ disabled_plugins = ["cri"]
 	}, cl, nil
 }
 
+func (c *Containerd) Close() error {
+	return nil
+}
+
 func formatLogs(m map[string]*bytes.Buffer) string {
 	var ss []string
 	for k, b := range m {