Update the `bandit` hook configuration for pre-commit

[mcdonnnj]

🗣 Description

This pull request updates the exclude definition for the bandit hook in our pre-commit configuration.

💭 Motivation and context

In #175 we removed the systemd_enabled scenario but we missed updating the pre-commit configuration. In addition to rectifying that mistake I also updated the exclude definition to blanket cover any molecule scenario's tests/ directory.

🧪 Testing

Automated tests pass. I verified with the check-useless-excludes meta hook from https://github.com/cisagov/skeleton-generic/pull/178 that it resolves to at least one file in the repository.

✅ Pre-approval checklist

• [x] This PR has an informative and human-readable title.
• [x] Changes are limited to a single goal - eschew scope creep!
• [x] All relevant type-of-change labels have been added.
• [x] I have read the CONTRIBUTING document.
• [x] These code changes follow cisagov code standards.
• [x] All new and existing tests pass.