Add github action to update the screenshot

.github/workflows/update-screenshot.yml

@@ -0,0 +1,35 @@
+on:
+  workflow_dispatch:
+  push:
+
+jobs:
+  update_screeshot:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v26
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+
+      - name: Install SSH key
+        uses: shimataro/ssh-key-action@v2
+        with:
+          key: ${{ secrets.GH_SSH_PRIVATE_KEY }}
+          known_hosts: $GH_PUB_KEY
+
+      - name: Get screenshot
+        run: |
+          nix build .\#screenshot-system.passthru.tests.qtile \
+            --print-build-logs -v \
+            --extra-experimental-features 'nix-command flakes'
+
+      - name: Push in gist
+        run: |
+          git clone [email protected]:9e1a986f1da9a1452e94103979c79aa4.git gist
+
+          cp result/terminal.png gist/screenshot.png
+          cd gist
+
+          git add -m "Update screenshot"
+          git push origin main