docs: fixed interpolation syntax

[bhavyakaria]

Pull Request

📖 Description

Fixed the interpolation syntax in the docs.

🎫 Issues

#6475

👩‍💻 Reviewer Notes

Found 2 occurrences where the syntax was incorrect. Have fixed it.

✅ Checklist

General

• [x] I have updated the project documentation to reflect my changes.
• [x] I have read the CONTRIBUTING documentation and followed the standards for this project.

[bhavyakaria]

@microsoft-github-policy-service agree

[janechu]

We've folded in your fix to users/janechu/update-docs-content, we're currently in progress on it for v2 of @microsoft/fast-element and your fix will be included.