Unify structure for ext/random's randomizer tests (#9410)

* Unify structure for ext/random's engine tests (2)

This makes adjustments that were missed in
2d6a883b3a1e5ee4f225dce6

Unify structure for ext/random's randomizer tests (#9410)

* Unify structure for ext/random's engine tests (2)

This makes adjustments that were missed in
2d6a883b3a1e5ee4f225dce64584ad2522e8e391.

* Add `engines.inc` for ext/random tests

* Unify structure for ext/random's randomizer tests

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