feat(ci): Add check and update workflows

.forgejo/workflows/check.yml

@@ -0,0 +1,37 @@
+name: Perform checks
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  formatting:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install nix
+        uses: https://github.com/DeterminateSystems/nix-installer-action@main
+      - name: Setup Action cache for nix
+        uses: https://github.com/DeterminateSystems/magic-nix-cache-action@main
+        with:
+          fail-mode: true
+      - name: Check Nix flake inputs
+        uses: https://github.com/DeterminateSystems/flake-checker-action@v4 # This action
+      - name: Run nix fmt
+        run: nix fmt -- --check .
+
+  nix_flake_check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install nix
+        uses: https://github.com/DeterminateSystems/nix-installer-action@main
+      - name: Setup Action cache for nix
+        uses: https://github.com/DeterminateSystems/magic-nix-cache-action@main
+        with:
+          fail-mode: true
+      - name: Check Nix flake inputs
+        uses: https://github.com/DeterminateSystems/flake-checker-action@v4 # This action
+      - name: Run nix flake check
+        run: nix flake check

.forgejo/workflows/update.yml

@@ -0,0 +1,84 @@
+name: Update `flake.lock`
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '0 0 * * 0' # runs weekly on Sunday at 00:00
+
+jobs:
+  update_lockfile:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Install nix
+        uses: https://github.com/DeterminateSystems/nix-installer-action@main
+      - name: Setup Action cache for nix
+        uses: https://github.com/DeterminateSystems/magic-nix-cache-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.yml][1] with the help of
+            [create-pull-request][2].
+
+            [1]: https://forgejo.stefka.eu/jiriks74/nix.nvim/src/branch/main/.github/workflows/update.yml
+            [2]: https://forgejo.stefka.eu/jiriks74/create-pull-request
+
+      - name: Generate PR body
+        uses: pedrolamas/handlebars-action@v2.4.0 # v2.4.0
+        with:
+          files: "pr_body.template"
+          output-filename: "pr_body.md"
+      - name: Save PR body
+        id: pr_body
+        uses: 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
+        id: create-pull-request
+        uses: https://forgejo.stefka.eu/jiriks74/create-pull-request@7174d368c2e4450dea17b297819eb28ae93ee645
+        with:
+          token: ${{ secrets.FORGEJO_TOKEN_FOR_UPDATES  }}
+          body: ${{ steps.pr_body.outputs.content }}
+          author: '"github-actions[bot]" <github-actions[bot]@users.noreply.github.com>'
+          title: 'automated: Update `flake.lock`'
+          commit-message: |
+            automated: Update `flake.lock`
+
+            ${{ steps.pr_body.outputs.content }}
+
+          branch: update-flake-lock
+          delete-branch: true
+      - name: Print PR number
+        run: |
+          echo "Pull request number is ${{ steps.create-pull-request.outputs.pull-request-number }}."
+          echo "Pull Request URL - ${{ steps.cpr.outputs.pull-request-url }}"