Add stylelint ci check

Signed-off-by: Julius Härtl <jus@bitgrid.net>

.github/workflows/lint.yml

@@ -43,3 +43,25 @@ jobs:
         run: npm ci
       - name: ESLint
         run: npm run lint
+
+  stylelint:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-versions: [12.x]
+
+    name: stylelint node${{ matrix.node-versions }}
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Set up node ${{ matrix.node-versions }}
+        uses: actions/setup-node@v1
+        with:
+          node-versions: ${{ matrix.node-versions }}
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Lint
+        run: npm run stylelint