add flake update workflow and change to use local mirror of actions

.forgejo/workflows/flake-update.yaml

@@ -1,3 +1,4 @@
+name: Update .lock file
 on:
   push:
     branches:
@@ -5,12 +6,23 @@ on:
   schedule:
     - cron: '0 2 * * *'
 jobs:
-  test:
-    runs-on: docker
+  flake-update:
     steps:
-      - uses: actions/checkout@v4
-      - name: update flake
-        run: |
-        nix flake update --experimental-features 'nix-command flakes'
+      - name: Checkout repository
+        uses: Ittihadyya/checkout@v4
+      - name: Install nix
+        uses: Ittihadyya/nix-installer-action@v16
+      - name: Update flake.lock
+        uses: Ittihadyya/update-flake-lock@v24
+        with:
+          commit-msg: "Update flake.lock"
+          pr-title: "Update flake.lock"
+          pr-body: |
+            ```
+            {{ env.GIT_COMMIT_MESSAGE }}
+            ```
+          pr-labels: |
+            dependencies
+            automated