cmake: fix cython target in test/CMakeFile.txt

cmake: fix cython target in test/CMakeFile.txt

The cython target is called cython_modules in python2 environments and
cython3_modules in python3 environments. Reflect that naming in
src/test/CMakeFile.txt. Otherwise the test target can not build in
python3 environments.

Signed-off-by: Jan Fajerski <jfajerski@suse.com>
(cherry picked from commit 743b9108c0f217ef6eeaadf645a538991e7d5eff)

Conflicts:
  src/test/CMakeLists.txt - Resovled by changing line 548 to
  "cython${PY_BINDING_INFIX}_modules)" and picking no other changes.