Update CONTRIBUTING.md

[artsiom-dorakhau]

Description

Fixed a small typo in the document.

Motivation and Context

Improves clarity and correctness; no functional changes.

How Has This Been Tested?

No tests required—this change is non-functional and affects only text.

Screenshots (if appropriate):

Types of Changes

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.