Retry the CI Build job's docker build on transient Docker Hub timeouts

The Build job's `make docker` step boots buildkit by pulling moby/buildkit
from Docker Hub, which intermittently times out on shared runners
("Client.Timeout exceeded while awaiting headers"). Retry once, mirroring the
existing `make docker.push || make docker.push` pattern in publish-docker.yaml.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: wu-sheng

.github/workflows/CI.yaml

@@ -84,7 +84,10 @@ jobs:
         run: make build -j3
 
       - name: Build Docker images
-        run: make docker
+        # Retry once: booting buildkit pulls moby/buildkit from Docker Hub, which
+        # intermittently times out on shared runners. Mirrors publish-docker.yaml's
+        # `make docker.push || make docker.push`.
+        run: make docker || make docker
 
 
   command-tests: