deps: update gax.version to v2.20.1 (#937)

Author: renovate-bot

first-party-dependencies/pom.xml

@@ -56,7 +56,7 @@
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <site.installationModule>${project.artifactId}</site.installationModule>
     <grpc.version>1.51.0</grpc.version>
-    <gax.version>2.19.5</gax.version>
+    <gax.version>2.20.1</gax.version>
     <grpc-gcp.version>1.3.2</grpc-gcp.version>
     <gson.version>2.10</gson.version>
     <guava.version>31.1-jre</guava.version>