Markdownlint: Fix TOP009 errors in existing custom rule test files

[mao-sz]

Because

TOP001-008 had test files that omitted trailing periods in LO items, now enforced by TOP009. These ought to be fixed so any future changes to those rules would have their test files flag errors only for the custom rule being tested.

This PR

• Adds trailing period to TOP001-008 test files' LO items as necessary.
• Disables TOP008 for an intentional violation in the TOP006 test file to reduce error noise.

Issue

N/A

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide

[ManonLef]

Thank you!