ci: fix PRs not merged automatically redux (#1212)

To match nixos-anywhere's setup :)

.github/workflows/auto-merge.yml

@@ -1,11 +1,6 @@
 name: Auto Merge Dependency Updates
 on:
-  pull_request_target:
-    types:
-      - opened
-      - synchronize
-      - reopened
-      - labeled
+  - pull_request_target
 jobs:
   auto-merge-dependency-updates:
     runs-on: ubuntu-latest
@@ -17,5 +12,3 @@ jobs:
       cancel-in-progress: true
     steps:
       - uses: Mic92/auto-merge@main
-        with:
-          required-labels: merge-queue,dependencies

.github/workflows/update-flake-lock.yml

@@ -1,21 +1,30 @@
-name: update-flake-lock
+name: "Update flakes"
 on:
-  workflow_dispatch: # allows manual triggering
+  workflow_dispatch:
   schedule:
-    - cron: '0 0 * * 1,4' # Run twice a week
-permissions:
-  pull-requests: write
-  contents: write
+    - cron: "0 0 * * 1,4"
+
 jobs:
-  lockfile:
+  createPullRequest:
     runs-on: ubuntu-latest
     steps:
-      - name: Checkout repository
-        uses: actions/checkout@v6
+      - uses: actions/checkout@v6
       - name: Install Nix
         uses: cachix/install-nix-action@v31
-      - name: Update flake.lock
-        uses: DeterminateSystems/update-flake-lock@v28
         with:
-          pr-labels: |
-            merge-queue
+          extra_nix_config: |
+            access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+      - uses: actions/create-github-app-token@v1
+        id: app-token
+        with:
+          app-id: ${{ vars.APP_ID }}
+          private-key: ${{ secrets.APP_PRIVATE_KEY }}
+      - name: Update flakes
+        run: nix flake update
+      - name: Create Pull Request
+        uses: peter-evans/create-pull-request@v7
+        with:
+          title: "flake: update inputs"
+          token: ${{ steps.app-token.outputs.token }}
+          labels: |
+            auto-merge