ci: add flake auto-update workflow

Signed-off-by: Roman Volosatovs <[email protected]>

.github/workflows/update.yml

@@ -0,0 +1,29 @@
+name: Update
+
+on:
+  schedule:
+    - cron: "0 0 * * *"
+  workflow_dispatch:
+
+jobs:
+  nix-update:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: nixbuild/nix-quick-install-action@v19
+        with:
+          nix_conf: |
+            experimental-features = nix-command flakes
+            access-tokens = github.com=${{ github.token }}
+      - uses: jessestricker/nix-flake-update@v1
+        id: nix-update
+      - uses: peter-evans/create-pull-request@v4
+        with:
+          branch: nix-update
+          commit-message: "build(nix): update flake lock"
+          title: "build(nix): update flake lock"
+          body: ${{ steps.nix-update.outputs.pull-request-body }}
+          labels: dependencies, nix
+          assignees: |
+            rvolosatovs
+          signoff: true