chore: Test with Protobuf-Java v4.32 [no need to review]

Author: lqiu96

.kokoro/build.sh

@@ -75,6 +75,7 @@ integration)
 
     mvn -B ${INTEGRATION_TEST_ARGS} \
       -ntp \
+      -Dprotobuf.version=4.32.0 \
       -Penable-integration-tests \
       -DtrimStackTrace=false \
       -Dclirr.skip=true \