Validate composer.json in CI

Author: theodorejb

.github/workflows/php.yml

@@ -45,6 +45,9 @@ jobs:
       - name: Setup problem matchers for PHPUnit
         run: echo "::add-matcher::${{ runner.tool_cache }}/phpunit.json"
 
+      - name: Validate composer.json and composer.lock
+        run: composer validate --strict
+
       - name: Install Composer dependencies
         run: composer install --no-progress