ci: Add update-playground action

.github/workflows/update-playground.yml

@@ -0,0 +1,37 @@
+name: Update playground
+
+on:
+  - workflow_dispatch
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+        with: { submodules: true }
+      - uses: actions/setup-node@v4
+        with: { node-version: 20 }
+      - run: npm ci
+      - run: npm run build:browser
+      - name: Playground setup
+        working-directory: ./playground
+        run: npm ci
+      - name: Playground build
+        working-directory: ./playground
+        run: npm run build
+
+      - uses: actions/checkout@v4
+        with:
+          repository: eemeli/yaml-playground
+          ref: gh-pages
+          path: ./gh-pages
+      - run: rm gh-pages/*
+      - run: cp playground/site/* gh-pages/
+
+      - name: git config
+        run: |
+          git config --global user.name "github-actions[bot]"
+          git config --global user.email "41898282+github-actions[bot]@users.noreply.github.com"
+      - run: git add . && git commit -m 'Update playground' && git push
+        working-directory: ./gh-pages