add timeout test case to xds interop tests (#7888)

diff --git a/buildscripts/kokoro/xds.sh b/buildscripts/kokoro/xds.sh
index bd5b947..fa72773 100755
--- a/buildscripts/kokoro/xds.sh
+++ b/buildscripts/kokoro/xds.sh
@@ -28,10 +28,10 @@
 # --test_case after they are added into "all".
 JAVA_OPTS=-Djava.util.logging.config.file=grpc-java/buildscripts/xds_logging.properties \
   python3 grpc/tools/run_tests/run_xds_tests.py \
-    --test_case="all,path_matching,header_matching,circuit_breaking" \
+    --test_case="all,path_matching,header_matching,circuit_breaking,timeout" \
     --project_id=grpc-testing \
     --project_num=830293263384 \
-    --source_image=projects/grpc-testing/global/images/xds-test-server-3 \
+    --source_image=projects/grpc-testing/global/images/xds-test-server-4 \
     --path_to_server_binary=/java_server/grpc-java/interop-testing/build/install/grpc-interop-testing/bin/xds-test-server \
     --gcp_suffix=$(date '+%s') \
     --verbose \