[stable21] Add stylelint to github actions

.github/workflows/lint-stylelint.yml

@@ -0,0 +1,44 @@
+# This workflow is provided via the organization template repository
+#
+# https://github.com/nextcloud/.github
+# https://docs.github.com/en/actions/learn-github-actions/sharing-workflows-with-your-organization
+
+name: Lint
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+      - stable*
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    name: stylelint
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Read package.json node and npm engines version
+        uses: skjnldsv/read-package-engines-version-actions@v1.1
+        id: versions
+        with:
+          fallbackNode: '^12'
+          fallbackNpm: '^6'
+
+      - name: Set up node ${{ steps.versions.outputs.nodeVersion }}
+        uses: actions/setup-node@v2
+        with:
+          node-version: ${{ steps.versions.outputs.nodeVersion }}
+
+      - name: Set up npm ${{ steps.versions.outputs.npmVersion }}
+        run: npm i -g npm@"${{ steps.versions.outputs.npmVersion }}"
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Lint
+        run: npm run stylelint