Fix formatting and phrasing in Japanese documentation

[hyoshioka0128]

Purpose

Corrected minor formatting and phrasing issues in the Japanese documentation for creating a Visual Studio Code Chat Copilot agent using GitHub Models Phi-3.5.

https://github.com/microsoft/PhiCookBook/blob/main/translations/ja/md/02.Application/02.Code/Phi3/CreateVSCodeChatAgentWithGitHubModels.md

related Azure/co-op-translator#240

#PingMSFTDocs

Does this introduce a breaking change?

When developers merge from main and run the server, azd up, or azd deploy, will this produce an error?
If you're not sure, try it out on an old environment.

[ ] Yes
[x] No

Does this require changes to learn.microsoft.com docs?

This repository is referenced by (https://azure.microsoft.com/products/phi-3)
which includes deployment, settings and usage instructions.

[ ] Yes
[x] No

Type of change

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[x] Documentation content changes
[ ] Other... Please describe: