Improve our CI to include testing with supported Node.js

[infomiho]

Before Wasp 0.12 we only supported Node.js 18 and we based our tests in the CI on using the Node.js 18.

From Wasp 0.12 we support Node.js >= 18 and our tests should check if our code works for at least one other version > 18 to ensure things like this: https://github.com/wasp-lang/wasp/issues/1833 don't slip by.

[Zeko369]

Hmm, we could also include the "latest" so current 21.X at the time of running the ci + LTS/Current (so 18 and 20)

[infomiho]

Completed by #1836