github PR build permissions

[aledsage]

Attempt to fix error on PRs, for when github workflow automatically adds comments on PR:

   data: {
      message: 'Resource not accessible by integration',
      documentation_url: 'https://docs.github.com/rest/issues/comments#create-an-issue-comment',
      status: '403'
    }
    ...
    Error: Unhandled error: HttpError: Resource not accessible by integration

This is the fix suggested by @ivan-gudak

[aledsage]

Perhaps this fix is not enough: with this commit in the branch, PR #13 still failed with the same error: https://github.com/dynatrace-oss/dynatrace-managed-mcp/actions/runs/20232239832/job/58077863611?pr=13

Or would the new configuration only get applied to PR builds once this is merged to main?