build: Substitute relative with absolute path in test
Fix unit test GivenOSCCatalog_WhenConvertingToMantle_ThenCheckExpectedValues in engine/tests/Conversion/OscToMantle/ConvertScenarioEnvironmentTest.cpp.
Pipeline: https://ci.eclipse.org/openpass/job/OpenScenarioEngine/job/MR-194/
Edited by Lorenzo Appino