Update large gh import spec test data json

What does this MR do and why?

Describe in detail what your merge request does and why.

Make the structure of data.json more generic.

This is needed to be able to reuse the same json structure for other importer tests.

This change has no effect on any test running in Gitlab project since this spec is executed in entirely different project on a nightly basis.

MR acceptance checklist

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