Add workflows

.github/workflows/flake-check.yaml

@@ -0,0 +1,14 @@
+name: Run nix flake check
+on:
+  push:
+  pull_request:
+
+jobs:
+  flake-check:
+    runs-on: ubuntu-latest
+    container:
+      image: ghcr.io/catthehacker/ubuntu:runner-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: cachix/install-nix-action@v27
+      - run: nix flake check

.github/workflows/flake-update.yaml

@@ -0,0 +1,25 @@
+---
+name: Periodic flake update
+on:  # yamllint disable-line rule:truthy
+  schedule:
+    - cron: "0 0 * * *"
+
+permissions:
+  contents: write
+
+jobs:
+  flake-update:
+    runs-on: ubuntu-latest
+    container:
+      image: ghcr.io/catthehacker/ubuntu:runner-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: cachix/install-nix-action@v27
+      - name: configure git
+        run: |
+          git config --global user.name 'torjus-bot'
+          git config --global user.email 'torjus-bot@git.t-juice.club'
+      - name: flake update
+        run: nix flake update --commit-lock-file
+      - name: push
+        run: git push