fix: correct testcase and solution according to readme.md

[tim48-robot]

Because the solution and testcase for number 2 does not match the requirements asked on readme.md

This PR

• Changed the solution and testing part of the file to match the readme.md to include the number 6.

Issue

Closes #XXXXX

Additional Information

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. 01_helloWorld: Update test cases
• 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 this PR includes any changes that affect the solution of an exercise, I've also updated the solution in the /solutions folder

[MaoShizhong]

This change isn't correct because the instructions want you to return false when the number is less than 10, meaning 6 should return false.
The current solution and tests are fine.