Laravel 13 support

[louisbels]

Follows the same pattern as #32 (Laravel 12 support) — just bumps version constraints.

Changes

• composer.json: add ^13.0 to laravel/framework, ^11.0 to orchestra/testbench, ^12.0 to phpunit/phpunit
• .github/workflows/run_tests.yml: add 13.* to the matrix with testbench: ^11.0, and exclude PHP 8.1/8.2 for L13 (L13 requires PHP 8.3+)

Verified locally

Tests pass on PHP 8.4 + Laravel 13.6.0 + PHPUnit 12.5.23:

OK (2 tests, 2 assertions)