[Bot] Fix backport bot (#5681)

Apparently changing the GH Token made it lose permission... error from
here:
https://github.com/paritytech/polkadot-sdk/actions/runs/10815755374/job/30005387859

From this list it looks like comment creation should be allowed by
adding issues to the list:
https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/controlling-permissions-for-github_token