Update github.com/googleapis/gnostic to v0.5.5 and updating transitive dependencies go-cmp, protobuf,, to adapt the latest gnostic release which cosists of [Update protos for Go protoc plugin compatibility]

vendor/github.com/googleapis/gnostic/compiler/helpers.go

@@ -176,6 +176,8 @@ func StringForScalarNode(node *yaml.Node) (string, bool) {
 			return node.Value, true
 		case "!!str":
 			return node.Value, true
+		case "!!timestamp":
+			return node.Value, true
 		case "!!null":
 			return "", true
 		default:
@@ -241,6 +243,15 @@ func InvalidKeysInMap(m *yaml.Node, allowedKeys []string, allowedPatterns []*reg
 	return invalidKeys
 }
 
+// NewNullNode creates a new Null node.
+func NewNullNode() *yaml.Node {
+	node := &yaml.Node{
+		Kind: yaml.ScalarNode,
+		Tag:  "!!null",
+	}
+	return node
+}
+
 // NewMappingNode creates a new Mapping node.
 func NewMappingNode() *yaml.Node {
 	return &yaml.Node{