Revert "update guava version"

This reverts commit a24f8f8.

Author: JoeWang1127

gapic-generator-java-pom-parent/pom.xml

@@ -30,7 +30,7 @@
     <google.auth.version>1.23.0</google.auth.version>
     <google.http-client.version>1.44.1</google.http-client.version>
     <gson.version>2.10.1</gson.version>
-    <guava.version>33.2.0-jre</guava.version>
+    <guava.version>33.1.0-jre</guava.version>
     <protobuf.version>3.25.3</protobuf.version>
     <opentelemetry.version>1.38.0</opentelemetry.version>
     <maven.compiler.release>8</maven.compiler.release>