Add workflow for updating Nix dependencies

.github/workflows/main.yml

@@ -0,0 +1,24 @@
+name: "Flake.lock: update Nix dependencies"
+
+on:
+  workflow_dispatch: # allows manual triggering
+  schedule:
+    - cron: '0 16 * * *' # runs weekly on Sunday at 00:00
+
+jobs:
+  nix-flake-update:
+    permissions:
+      contents: write
+      id-token: write
+      issues: write
+      pull-requests: write
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: DeterminateSystems/determinate-nix-action@v3
+      - uses: DeterminateSystems/update-flake-lock@main
+        with:
+          pr-title: "Update Nix flake inputs"
+          pr-labels: |                  
+            dependencies
+            automated