CI: add reusable actions

.github/workflows/nix-update-inputs.yml

@@ -0,0 +1,37 @@
+name: Nix
+
+on:
+  schedule:
+    - cron: '0 0 * * *' # check daily
+
+jobs:
+  update:
+    name: inputs
+    runs-on: ubuntu-latest
+    steps:
+      - name: Clone repository
+        uses: actions/checkout@v3
+        with:
+          token: ${{ secrets.PAT }}
+
+      - name: Install nix
+        uses: cachix/install-nix-action@v22
+        with:
+          install_url: https://nixos.org/nix/install
+          extra_nix_config: |
+            auto-optimise-store = true
+            access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+            experimental-features = nix-command flakes
+
+      - name: Update inputs
+        run: nix/update-inputs.sh
+
+      - name: Commit
+        uses: stefanzweifel/git-auto-commit-action@v4
+        with:
+          commit_message: "[gha] Nix: update inputs"
+
+  update-build:
+    needs: update
+    uses: ./.github/workflows/nix-build.yml
+    secrets: inherit