Add prettier job to GitHub Actions

Author: wojtekmaj

.github/workflows/ci.yml

@@ -41,6 +41,37 @@ jobs:
       - name: Run tests
         run: yarn lint
 
+  prettier:
+    name: Prettier
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Cache .yarn/cache
+        uses: actions/cache@v3
+        env:
+          cache-name: yarn-cache
+        with:
+          path: .yarn/cache
+          key: ${{ runner.os }}-${{ env.cache-name }}-${{ hashFiles('**/yarn.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-${{ env.cache-name }}
+
+      - name: Use Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: '16'
+
+      - name: Install dependencies
+        run: yarn --immutable
+        env:
+          HUSKY: 0
+
+      - name: Prettier
+        run: yarn prettier
+
   unit:
     name: Unit tests
     runs-on: ubuntu-latest