Update GCP runner, proxy, prometheus, and node-exporter images to version 20260518.834

This PR updates the runner, proxy, prometheus, and node-exporter image references in locals.tf to use the latest images:
- Runner: us-docker.pkg.dev/gitpod-next-production/gitpod-next/gitpod-gcp-runner:20260518.834
- Proxy: us-docker.pkg.dev/gitpod-next-production/gitpod-next/gitpod-proxy:20260518.834
- Prometheus: us-docker.pkg.dev/gitpod-next-production/gitpod-next/prometheus:v3.11.3
- Node-exporter: us-docker.pkg.dev/gitpod-next-production/gitpod-next/node-exporter:v1.11.1

Auto-generated by: https://github.com/gitpod-io/gitpod-next/actions/runs/26037789022

Author: gitpod-next-automation

locals.tf

@@ -18,8 +18,8 @@ locals {
   })
 
   # Default images
-  default_runner_image = "us-docker.pkg.dev/gitpod-next-production/gitpod-next/gitpod-gcp-runner:20260518.759"
-  default_proxy_image  = "us-docker.pkg.dev/gitpod-next-production/gitpod-next/gitpod-proxy:20260518.759"
+  default_runner_image = "us-docker.pkg.dev/gitpod-next-production/gitpod-next/gitpod-gcp-runner:20260518.834"
+  default_proxy_image  = "us-docker.pkg.dev/gitpod-next-production/gitpod-next/gitpod-proxy:20260518.834"
 
   default_prometheus_image    = "us-docker.pkg.dev/gitpod-next-production/gitpod-next/prometheus:v3.11.3"
   default_node_exporter_image = "us-docker.pkg.dev/gitpod-next-production/gitpod-next/node-exporter:v1.11.1"