forgejo-runner: update flake nightly

.forgejo/workflows/nightly-update.yaml

@@ -0,0 +1,22 @@
+on: 
+  schedule:
+    - cron: 0 3 * * *
+  
+jobs:
+  UpdateFlake:
+    runs-on: native
+
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v4
+      - name: Update flake
+        run: | 
+          cd ${{ gitea.workspace }}
+          nix flake update
+      - name: Commit new Flake.lock
+        run: |
+          git config --local user.email "christoph.hollizeck@hey.com"
+          git config --local user.name "forgjo-actions[bot]"
+          git commit -a -m "chore: update flake"
+      - name: Push changes
+        run: git push