fix: ninja listings

[danielsp45]

No description provided.

[reviewpad]

AI-Generated Summary: This pull request introduces changes to both source code and tests. The modifications to the BokkenWeb.SkillJSON source file refactor the handling of skills, removing unnecessary step of wrapping skills in a map for function data(). The change seems to simplify the code logic and leads to lesser clutter.

In the test files ninja_json_test.exs and skill_json_test.exs, the changes insert stubbed data to the tests using insert() and insert_list() instead of build functions. This change allows actual creation of test data to serve the purpose of proper testing. Also, a new test case is being added to the Bokken.NinjaJSONTest. This new test case appears to be empty as of now but can be filled with relevant assertions or validations in the future.

In summary, this pull request brings simplifications and enhancements to both the source code and tests in the application.