Change loading phpdotenv from createUnsafeImmutable to createUnsafeMu…

…table

Realistically this mainly affects values in .env (which uses putenv). Values written to $_SERVER globally (which App::env() checks) aren’t affected.

bootstrap.php

@@ -12,7 +12,9 @@
 
 // Load dotenv?
 if (class_exists('Dotenv\Dotenv')) {
-    Dotenv\Dotenv::createUnsafeImmutable(CRAFT_BASE_PATH)->safeLoad();
+    // By default, this will allow .env file values to override environment variables
+    // with matching names. Use `createUnsafeImmutable` to disable this.
+    Dotenv\Dotenv::createUnsafeMutable(CRAFT_BASE_PATH)->safeLoad();
 }
 
 // Define additional PHP constants