test: streamline use of NameGeneratorTestingEnvironment

[skaldarnar]

An attempt to address MovingBlocks/Terasology#4598 (comment)

CreatureNameProviderTest uses a HeadlessEnvironment, but for some reason does not make use of NameGeneratorTestingEnvironment as the other test classes there. That testing environment has more elaborate code in its setUpClass method:

https://github.com/Terasology/NameGenerator/blob/develop/src/test/java/org/terasology/namegenerator/NameGeneratorTestingEnvironment.java#L28-L46

Maybe this explains why this one test is failing with NUI v3.0.

I'm super confused which of those tests actually require a headless environment and which don't, to be honest.

[skaldarnar]

I think I've tested the following combinations now :face_with_monocle:

Result	MovingBlocks/Terasology	Terasology/NameGenerator
✔️	develop	develop
✔️	develop	test/consistent-use-of-testing-environment
❌	nui-gestalt-separation	develop
✔️	nui-gestalt-separation	test/consistent-use-of-testing-environment

[keturn]

NameGeneratorTestingEnvironment doesn't look like it is wrong to use here, so sure. 👍

(still confused about how this could be somehow tied to NUI versions)