integration_test fails on pull_request_review events due to unauthorized GHCR package push

### Bug Description

- When `upload-image` is not explicitly set, `fromFork()` checks `context.eventName === 'pull_request'`.
- When the workflow is triggered by `pull_request_review` (e.g. on approval in our [workflow example](https://github.com/canonical/kernelfactory.canonical.com/actions/runs/32028950313/job/95384522737?pr=586)), `context.eventName` is `'pull_request_review'`.
- `fromFork()` returns false, causing operator-workflows to default to registry (ghcr.io).
- In GitHub Actions, standard `GITHUB_TOKEN` credentials in workflow runs triggered by PR review events do not have permissions to write/create packages causing a message `denied: installation not allowed to Create organization package error.`

https://github.com/canonical/operator-workflows/blob/5ddf42a5a7133f29db743d8956c38646db736699/src/plan.ts#L22-L31

### Impact

Medium (functionality degraded, workaround exists)

### Impact Rationale

_No response_

### Link to the failing workflow

https://github.com/canonical/kernelfactory.canonical.com/actions/runs/32110091517/job/95627558080

### Additional context

_No response_

Start with src/plan.ts around lines 22-31 and inspect how fromFork() handles pull_request_review events. Reproduce or run the integration test using the linked workflow context, then verify that the workflow no longer attempts an unauthorized GHCR package push and that the integration test passes.

Written by the indexing model from the issue text.