Added tokens for github pages workflow

[janechu]

Pull Request

📖 Description

The repository does not have permissions to add commits to a branch on GitHub, this adds to the github pages deploy workflow the same tokens used for npm package publishing which must perform a similar action and so should work.

👩‍💻 Reviewer Notes

Initial attempt at manually running the workflow ended in a 403, in theory this change should grant the permissions needed to apply commits to the gh-pages branch.

✅ Checklist

General

• I have included a change request file using $ yarn change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.