TEST: updated test_sct_register_multimodal.py
TEST: updated test_sct_register_multimodal.py

Former-commit-id: acf7623d776f57a60998e87e497f264834b27e25
Former-commit-id: aa2ec31772e4f301e7d9761c6381af69d880dd41
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox