ci: add update-flake-lock workflow (#1424)

Signed-off-by: Sora Morimoto <[email protected]>

.github/workflows/update-flake-lock.yml

@@ -0,0 +1,21 @@
+name: Update Nix Flake Lock
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: 0 0 * * 0
+
+jobs:
+  lockfile:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v30
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      - uses: DeterminateSystems/update-flake-lock@v24
+        with:
+          pr-labels: |
+            dependencies
+            no changelog