ci: add workflow to update inputs every two weeks (#160)

.github/workflows/update-inputs.yml

@@ -0,0 +1,26 @@
+name: "Flake.lock: update Nix dependencies"
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: "0 0 1,15 * *" # runs at 00:00 on the 1st and 15th of each month
+
+jobs:
+  nix-flake-update:
+    name: "Update Nix flake inputs"
+    permissions:
+      contents: write
+      id-token: write
+      issues: write
+      pull-requests: write
+
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - uses: DeterminateSystems/determinate-nix-action@v3
+      - uses: DeterminateSystems/update-flake-lock@e637603d31bed83169f2e56bb475c9dff7af6544
+        with:
+          pr-title: "Update Nix flake inputs"
+          pr-labels: |
+            dependencies
+            automated