chore: add test:FixturePackageData target to generate Go fixtures

[lebauce]

Description

Adding a field to the types.Package - such as InstalledFiles require some tests
to be updated by modifying the Go structure used to compare against the results.
This PR has a mage target to automatically generate these Go structures.

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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).
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[lebauce]

Waiting for #5488 to be merged first

[knqyf263]

Thanks for your great work. It looks awesome, but this sort of test should be covered by integration tests or E2E tests in the first place. I've replaced the test with the mock in this PR, and then this change is no longer needed. But thanks again for your effort.