Fixes a typo in Japanese language

[momoto]

Description

Update CONTIRBUTING.ja.md to fix a typo in Japanese language. There is no issue number.

Motivation and Context

To avoid misleading the Japanese speakers by correcting a wrong Kanji character.

Types of changes

• Change to the site (I am attaching a screenshot showing the before and after)
• Code example added (and I also added the example to all translated languages)
• Improved translation
• Added new translation (and I also added a notice to each document missing translation)

Checklist

• I have read the contributing document.
• I have used hugo to render the site/docs locally and I am sure it works.

[CLAassistant]

All committers have signed the CLA.

[harsha509]

Thank you @momoto !