Advanced Selectors: adding a disclaimer on the usage of single colon vs double

[ht-l1]

Because

Adding two sentences to clarify the updated use of double colon.

This PR

In the Lesson Advanced Selector and under Assignment section Bullet two: adding two sentences to clarify the updated use of double colon.

Issue

Closes #26466

Additional Information

Closing pull request #26480, and replacing with this new one to get around the auto formatter.

Pull Request Requirements

• I have thoroughly read and understand The Odin Project 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
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• If any lesson files are included in this PR, they follow the Layout Style Guide

[wise-king-sullyman]

Looks great, thank you!