update vendor

Signed-off-by: Roland.Ma <rolandma@yunify.com>

vendor/github.com/deislabs/oras/pkg/context/context.go

@@ -0,0 +1,9 @@
+package context
+
+import "context"
+
+// Background returns a default context with logger discarded.
+func Background() context.Context {
+	ctx := context.Background()
+	return WithLoggerDiscarded(ctx)
+}