Add workflow to update flake inputs

.forgejo/workflows/update-flake-inputs.yaml

@@ -0,0 +1,76 @@
+name: Update `flake.lock`
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '0 0 * * 6' # runs weekly on Saturday at 00:00
+
+jobs:
+  update_lockfile:
+    runs-on: docker
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Install nix
+        uses: https://github.com/DeterminateSystems/nix-installer-action@main
+
+      - name: Update flake.lock
+        id: update
+        run: |
+          nix flake update 2> >(tee /dev/stderr) | awk '
+            /^• Updated input/ {in_update = 1; print; next}
+            in_update && !/^warning:/ {print}
+            /^$/ {in_update = 0}
+          ' > update.log
+
+          echo "UPDATE_LOG<<EOF" >> $GITHUB_ENV
+          cat update.log >> $GITHUB_ENV 
+          echo "EOF" >> $GITHUB_ENV
+
+          rm update.log
+
+      - name: Write PR body template
+        uses: https://github.com/DamianReeves/write-file-action@v1.3
+        with:
+          path: pr_body.template
+          contents: |
+            - The following Nix Flake inputs were updated:
+
+            ```
+            ${{ env.UPDATE_LOG }}
+            ```
+
+            Auto-generated by [update-flake-inputs.yaml][1] with the help of
+            [create-pull-request][2].
+
+            [1]: https://git.peprolinbot.com/peprolinbot/frues-clan/src/branch/main/.forgejo/workflows/update-flake-inputs.yaml
+            [2]: https://forgejo.stefka.eu/jiriks74/create-pull-request
+
+      - name: Generate PR body
+        uses: https://github.com/pedrolamas/handlebars-action@v2.4.0
+        with:
+          files: "pr_body.template"
+          output-filename: "pr_body.md"
+      - name: Save PR body
+        id: pr_body
+        uses: https://github.com/juliangruber/read-file-action@v1
+        with:
+          path: "pr_body.md"
+
+      - name: Remove temporary files
+        run: |
+          rm pr_body.template
+          rm pr_body.md
+
+      - name: Create Pull Request
+        uses: https://github.com/maxking/forgejo-create-pr@main
+        with:
+          token: ${{ secrets.FORGEJO_TOKEN }}
+          base: 'main'
+          pr-branch: 'flake-update'
+          add-paths: '.'
+          commit-message: |
+            automated: Update `flake.lock`
+
+            ${{ steps.pr_body.outputs.content }}
+          pr-title: 'automated: Update `flake.lock`'
+          pr-body: ${{ steps.pr_body.outputs.content }}