extend TestBlackBox::fileDependencies

narf.cpp includes awesome.h
awesome.h includes magnificent.h
awesome.h and magnificent.h are not listed in the project.
Changing magnificent.h must trigger a rebuild of narf.cpp.

Task-number: QBS-566
Change-Id: Ib2df45ac550951b550ce4ba0e7519268d9123eda
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>