Add CI4 coding standards linter

.github/workflows/main.yml

@@ -0,0 +1,61 @@
+name: Coding Standards
+
+on:
+  push:
+    paths:
+      - '**.php'
+      - 'spark'
+      - '.github/workflows/test-coding-standards.yml'
+  pull_request:
+    paths:
+      - '**.php'
+      - 'spark'
+      - '.github/workflows/test-coding-standards.yml'
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  lint:
+    name: PHP ${{ matrix.php-version }} Lint with PHP CS Fixer
+    runs-on: ubuntu-22.04
+
+    strategy:
+      fail-fast: false
+      matrix:
+        php-version:
+          - '7.4'
+          - '8.0'
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-version }}
+          extensions: tokenizer
+          coverage: none
+
+      - name: Get composer cache directory
+        run: echo "COMPOSER_CACHE_FILES_DIR=$(composer config cache-files-dir)" >> $GITHUB_ENV
+
+      - name: Cache dependencies
+        uses: actions/cache@v3
+        with:
+          path: ${{ env.COMPOSER_CACHE_FILES_DIR }}
+          key: ${{ runner.os }}-${{ matrix.php-version }}-${{ hashFiles('**/composer.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-${{ matrix.php-version }}-
+            ${{ runner.os }}-
+
+      - name: Install dependencies
+        run: composer update --ansi --no-interaction
+
+      - name: Run lint on `app/`, `public/`
+        run: vendor/bin/php-cs-fixer fix --verbose --ansi --dry-run --config=.php-cs-fixer.no-header.php --using-cache=no --diff