Use powsybl-config-test in unit tests

[geofjamg]

• Do you want to request a feature or report a bug?
  Bug

• What is the current behavior?
  powsybl-config-classic is used not only in the Spring Boot jar but also in unit test. So unit tests might fail because dependent of the system config.

• What is the expected behavior?
  powsybl-config-test has to be used => see powsybl-case-server for hidding powsybl-config-classic in test scope.

• What is the motivation / use case for changing the behavior?
  Having unit test results not dependent of the system environnement.

• Please tell us about your environment:

  • PowSyBl Version: ...
  • OS Version: ...

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, spectrum, etc)

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