ensure latest collab docker runtime is used

Author: mmcky

.github/workflows/collab.yml

@@ -4,7 +4,7 @@ jobs:
   execution-checks:
     runs-on: "runs-on=${{ github.run_id }}/family=g4dn.2xlarge/image=ubuntu24-gpu-x64/disk=large"
     container:
-      image: docker://us-docker.pkg.dev/colab-images/public/runtime
+      image: docker://us-docker.pkg.dev/colab-images/public/runtime:latest
       options: --gpus all
     steps:
       - uses: actions/checkout@v4