docs: fix sample code
docs: fix sample code

The namespace not starting with '\' will be prefixed with the default namespace.

bcit-ci/CodeIgniter4,kenjis/CodeIgniter4,kenjis/CodeIgniter4,kenjis/CodeIgniter4,bcit-ci/CodeIgniter4,bcit-ci/CodeIgniter4,bcit-ci/CodeIgniter4,kenjis/CodeIgniter4,kenjis/CodeIgniter4,bcit-ci/CodeIgniter4