Updates Changeset workflow (playcanvas#210)

* chore: update GitHub Actions workflow and package.json

- Added permissions for write access to contents and pull requests in the changesets workflow.
- Updated the fetch depth for the checkout step to ensure all history is available.
- Modified the publish command to use `pnpm -w changeset publish` and enabled GitHub releases.
- Cleaned up the package.json by removing the redundant `ci:publish` script.

* Apply suggestion from @Copilot

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>