test: use forked images

[knqyf263]

Description

The GHCR rate limits are applied to the entire aquasecurity organization, and currently the images for testing cannot be pulled, causing testing to fail. As a workaround, we are considering moving trivy-db to a separate organization or creating a separate organization for Trivy, but both of these measures need to be done after careful discussion with GitHub. So we will use the forked image as a temporary workaround until a solution is decided.

Related PRs

• test: define constants for test images #7739

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).