Update composer_83 test: ^8.3 may resolve to >=8.3 with newer PHP in manifest

Now that PHP 8.4+ is available, composer.json ^8.3 correctly resolves
to the latest 8.x (e.g. 8.4.20). Update assertions to accept any
PHP >=8.3 satisfying the ^8.3 constraint instead of pinning to 8.3.x.

Author: ivanovac