Fix test dependencies: scipy (#177)

Test require scipy, but this was never listed as dependency. Some upstream package seems to have dropped scipy as dependency.

https://github.com/PEtab-dev/libpetab-python/runs/8200033662?check_suite_focus=true

Author: dweindl

setup.py

@@ -74,7 +74,8 @@ def absolute_links(txt):
               'flake8',
               'pytest',
               'python-libcombine',
-              'simplesbml'
+              'simplesbml',
+              'scipy',
           ],
           'reports': ['Jinja2'],
           'combine': ['python-libcombine>=0.2.6'],