Add composer validation workflow

Author: pfefferle

.github/workflows/composer.yml

@@ -0,0 +1,29 @@
+name: Composer
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'composer.json'
+  pull_request:
+    paths:
+      - 'composer.json'
+  workflow_dispatch:
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.2'
+          tools: composer
+
+      - name: Validate composer.json
+        run: composer validate --strict
+
+      - name: Check dependencies
+        run: composer install --prefer-dist --no-progress --dry-run