🐛 Bug: No fallback behavior for action runs on forks

When this action runs on a fork and doesn't have permissions to fetch comments _(am I using the right terminology?)_, we see the dreaded `Resource not accessible by integration` error. Example from https://github.com/JoshuaKGoldberg/create-typescript-app/pull/1110 -> https://github.com/JoshuaKGoldberg/create-typescript-app/actions/runs/7297169422/job/19886082551?pr=1110:

```plaintext
Run github/accessibility-alt-text-bot@v1.4.0
Run source /home/runner/work/_actions/github/accessibility-alt-text-bot/v1.4.0/queries.sh
Detected bad alt text: true
Event type: pr_description
GraphQL: Resource not accessible by integration (addComment)
Error: Process completed with exit code 1.
```

This is a similar issue to https://github.com/mtfoley/pr-compliance-action/issues/368 -> https://github.com/mtfoley/pr-compliance-action/pull/374.

Suggestion: can the bot log an informative message in the error about what it _would_ post if it could? That way, if it's not able to actually post a comment, a useful error can still be logged.