add auto updater

.forgejo/workflows/update.yml

@@ -0,0 +1,38 @@
+name: Update Pins
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - rules.nix
+  schedule:
+    - cron: "0 6 * * *"
+  workflow_dispatch: {}
+
+jobs:
+  update:
+    runs-on: docker
+    container:
+      image: ghcr.io/catthehacker/ubuntu:runner-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Nix
+        uses: https://guardianproject.dev/actions/determinate-nix-action@v3
+
+      - name: Run update
+        run: nix run .#update
+
+      - name: Commit and push
+        run: |
+          git config user.name "forgejo-actions[bot]"
+          git config user.email "forgejo-actions[bot]@noreply.guardianproject.dev"
+          git add -A
+          if ! git diff --cached --quiet; then
+            git commit -m "update matrix-synapse pins"
+            git push
+          else
+            echo "No changes to commit"
+          fi