doc: clarify wsl kernel upgrade in docker_cpp_xpu_quickstart.md

[Civon]

Description

Clarify the wsl kernel selection. Feel free to edit. 🤗

What Changed

• Pinned the version of Microsoft's WSL guide.
• Instructed users to use the command git clone https://github.com/microsoft/WSL2-Linux-Kernel.git --depth=1 -b linux-msft-wsl-6.1.y instead of linux-msft-wsl-6.6.y as mentioned in the current MS guide.

Considerations

• The current MS guide uses version 6.6, which does not work.
• The previous MS commit used the main branch, which did not specify the v6.1 kernel.