vendor: update buildkit to v0.20.0-rc1

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

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

@@ -60,12 +60,14 @@ type Sandbox interface {
 	NewRegistry() (string, error)
 	Value(string) interface{} // chosen matrix value
 	Name() string
+	CDISpecDir() string
 }
 
 // BackendConfig is used to configure backends created by a worker.
 type BackendConfig struct {
 	Logs         map[string]*bytes.Buffer
 	DaemonConfig []ConfigUpdater
+	CDISpecDir   string
 }
 
 type Worker interface {