[CMake] require dynamic-graph-python v3.4.1
[CMake] require dynamic-graph-python v3.4.1

for dgpy.dgpyError in unit test introduced in 54d2c67d002597f9ca2d14055247d54e4881be03

stack-of-tasks/sot-core,stack-of-tasks/sot-core,stack-of-tasks/sot-core