Set credentials in GitHub Action

Author: jacobtomlinson

.github/workflows/update-kubernetes.yaml

@@ -18,6 +18,9 @@ jobs:
       - name: Install uv
         uses: astral-sh/setup-uv@v5
       - name: Update Kubernetes
+        env:
+          DOCKERHUB_USERNAME: ${{ secrets.DOCKERHUB_USERNAME }}
+          DOCKERHUB_TOKEN: ${{ secrets.DOCKERHUB_TOKEN }}
         run: uv run ./ci/update-kubernetes.py
       - name: Show diff
         id: diff