Enhancement: Run friendsofphp/php-cs-fixer on GitHub Actions

Co-authored-by: Markus Staab <maggus.staab@googlemail.com>

Closes GH-559.

.github/workflows/integrate.yaml

@@ -9,6 +9,49 @@ on:
       - "master"
 
 jobs:
+  coding-standards:
+    name: "Coding Standards"
+
+    runs-on: "ubuntu-latest"
+
+    strategy:
+      matrix:
+        php-version:
+          - "7.3"
+
+    steps:
+      - name: "Checkout"
+        uses: "actions/checkout@v3"
+
+      - name: "Set up PHP"
+        uses: "shivammathur/setup-php@v2"
+        with:
+          coverage: "none"
+          extensions: "none, json, mbstring, tokenizer"
+          php-version: "${{ matrix.php-version }}"
+
+      - name: "Set up problem matchers for PHP"
+        run: "echo \"::add-matcher::${{ runner.tool_cache }}/php.json\""
+
+      - name: "Validate composer.json and composer.lock"
+        run: "composer validate --ansi --strict"
+
+      - name: "Determine composer cache directory"
+        run: "echo \"COMPOSER_CACHE_DIR=$(composer config cache-dir)\" >> $GITHUB_ENV"
+
+      - name: "Cache dependencies installed with composer"
+        uses: "actions/cache@v3"
+        with:
+          path: "${{ env.COMPOSER_CACHE_DIR }}"
+          key: "php-${{ matrix.php-version }}-composer-${{ hashFiles('composer.lock') }}"
+          restore-keys: "php-${{ matrix.php-version }}-composer-"
+
+      - name: "Install dependencies with composer"
+        run: "composer install --ansi --no-interaction --no-progress"
+
+      - name: "Run friendsofphp/php-cs-fixer"
+        run: "vendor/bin/php-cs-fixer fix --ansi --config=.php-cs-fixer.php --diff --dry-run --verbose"
+
   tests:
     name: "Tests"