[Housekeeping] Fix Typos in CONTRIBUTING.md

[GeorgeLeithead]

Description of Change

There are a couple typo's in the markdown files.

Linked Issues

• Fixes = N/A

PR Checklist

• Has a linked Issue, and the Issue has been approved(bug) or Championed (feature/proposal)
• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard
• Documentation created or updated: https://github.com/MicrosoftDocs/CommunityToolkit/pulls

Additional information

• NO linked issue
• NO unit tests needed as only in markdown files.
• NO samples needed as only in markdown files.
• NO documentation needed as only in markdown files.

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

[TheCodeTraveler]

Thanks @GeorgeLeithead!

[GeorgeLeithead]

Thanks @GeorgeLeithead!

Spotted the mistakes when using it to write the CoPilot-instructions, and just couldn't leave them in there.