fix CI runs

.github/workflows/flake-update.yml

@@ -11,16 +11,11 @@ permissions:
 
 jobs:
   update:
-    runs-on: ubuntu-latest
+    runs-on: nix
     steps:
       - uses: actions/checkout@v4
 
-      - uses: cachix/install-nix-action@v31
-        with:
-          extra_nix_config: |
-            experimental-features = nix-command flakes
-
-      - run: nix flake update
+      - run: nix flake update -L
 
       - name: open/update PR
         env:
@@ -29,5 +24,5 @@ jobs:
           REPO: ${{ github.repository }}
         run: |
           printf 'Automated `nix flake update`.\n' > "$RUNNER_TEMP/body.md"
-          nix run .#ci -- open-pr \
+          nix run -L .#ci -- open-pr \
             flake-update "$GITHUB_REF_NAME" "flake.lock: update inputs" "$RUNNER_TEMP/body.md" automated