types: regenerate using latest protobuf v33 release

Change-Id: I4a786adbc7fc1a829e444dcaa0e43d35f42a3be4
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/713180
Reviewed-by: Chressie Himpel <chressie@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: stapelberg

integration_test.go

@@ -33,7 +33,7 @@ var (
 	regenerate   = flag.Bool("regenerate", false, "regenerate files")
 	buildRelease = flag.Bool("buildRelease", false, "build release binaries")
 
-	protobufVersion = "32.0"
+	protobufVersion = "33.0"
 
 	golangVersions = func() []string {
 		// Version policy: oldest supported version of Go, plus the version before that.