let dotenv overwrite existing variables

Author: transistive

tests/bootstrap_override_with_dotenv.php

@@ -14,4 +14,4 @@
 require __DIR__.'/../vendor/autoload.php';
 
 /** @psalm-suppress UncaughtThrowInGlobalScope */
-Dotenv::createImmutable(__DIR__.'/../')->load();
+Dotenv::createMutable(__DIR__.'/../')->load();