add permissions to the phpunit workflow

Author: michalsn

.github/workflows/phpunit.yml

@@ -18,6 +18,13 @@ on:
       - 'phpunit*'
       - '.github/workflows/phpunit.yml'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
 jobs:
   main:
     name: PHP ${{ matrix.php-versions }} - ${{ matrix.db-platforms }}