[RM-8093] Ambiguous definition of as_const method

Created on 2023-05-23 14:34:41 by Gaelle Daste. % Done: 100

Euclid :

• Elements 6.0.1 : C++14 -> as_const is only defined in our code (datatypes.h)
• Elements 6.1.1 : C++17 -> as_const is now ambiguous -> temporary fixed with adding @using namespace std@ in spectrum_test (only in SPE_RedshiftDeterminationLibrary)