clang-tidy: Ignored function return values in tests

[billpittman]

/data/ultifi/up-cpp/test/coverage/datamodel/UUriSerializerTest.cpp
/data/ultifi/up-cpp/test/coverage/datamodel/UuidSerializerTest.cpp

Several tests ignore function return values and that cause errors for clang-tidy.

[gregmedd]

std::ignore = calledFunction() seems to be the recommended way to deal with this.

[PLeVasseur]

Closed via #316