A potential Denial of Service issue in protobuf-java

Outdated `protobuf-java` found in [main/load-test-framework](https://github.com/GoogleCloudPlatform/pubsub/tree/master/load-test-framework):


Please update to the latest available versions of the following packages:

- protobuf-java (3.16.1, 3.18.2, 3.19.2)

[CVE-2021-22569](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-22569) High - CVSS Score: 7.5, An implementation weakness in how unknown fields are parsed in Java. A small (~800 KB) malicious payload can occupy the parser for several minutes by creating large numbers of short-lived objects that cause frequent, repeated GC pauses.