Change bing maps attribution link

[lukemckinstry]

Description

Updates attribution link for Bing maps

Issue number and link

https://github.com/CesiumGS/cesium/issues/12229

Testing plan

Verify link as described in issue

Author checklist

• [x] I have submitted a Contributor License Agreement
• [x] I have added my name to CONTRIBUTORS.md
• [ ] I have updated CHANGES.md with a short summary of my change
• [x] I have added or updated unit tests to ensure consistent code coverage
• [x] I have updated the inline documentation, and included code examples where relevant
• [x] I have performed a self-review of my code

[github-actions[bot]]

Thank you for the pull request, @lukemckinstry!

:white_check_mark: We can confirm we have a CLA on file for you.

[ggetz]

Fantastic, thanks @lukemckinstry!