Update image family (#2774)

agent_metrics/README.md

diff --git a/agent_metrics/README.md b/agent_metrics/README.md
index fb87f5d..d6d9ea0 100644
--- a/agent_metrics/README.md
+++ b/agent_metrics/README.md
@@ -13,7 +13,7 @@
     --machine-type n1-standard-1 \
     --zone us-central1-a \
     --image-project=ubuntu-os-cloud \
-    --image-family=ubuntu-1804-lts \
+    --image-family=ubuntu-2404-lts-amd64 \
     --scopes cloud-platform \
     --service-account buildkite-agent-metrics@bazel-public.iam.gserviceaccount.com \
     --metadata-from-file=startup-script=start.sh \