ci: use minimal GitHub Token permissions for docs workflow

[AdnaneKhan]

Issue #, if available: n/a

Notes

Scopes down GitHub token permissions to least necessary.

Checklist

Before you submit a pull request, please make sure you have the following:

• Code changes are compact and well-structured to facilitate easy review
• Changes are documented in the README.md and other relevant documentation pages
• PR title and description accurately reflect the changes and are detailed enough for historical tracking
• PR contains tests that cover all new code and the code has been manual tested
• All new dependencies are declared (if any), and no unnecessary libraries are added
• Performance impacts (if any) of the changes are evaluated and documented
• Security implications of the changes (if any) are reviewed and addressed
• I have read the Contributing Guidelines and agree to follow the Code of Conduct

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.