[CI] Fix macOS runners

[jfowkes]

Further investigation has revealed this to be what appears a genuine CUTEst bug in u/creport():

 >>> import pycutest
>>> p = pycutest.import_problem('BOX2')
0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 >>> 
>>> p.report()
{'f': 0, 'g': 5, 'H': 0, 'Hprod': 0, 'tsetup': 0.0, 'trun': 0.0, 'c': None, 'cg': None, 'cH': None}
0.000000 5.125000 0.000000 0.000000 0.000000 0.000000 0.000000 >>> p.report()
{'f': 0, 'g': 6, 'H': 0, 'Hprod': 0, 'tsetup': 0.0, 'trun': 0.0, 'c': None, 'cg': None, 'cH': None}
0.000000 6.812500 0.000000 0.000000 0.000000 0.000000 0.000000 >>> p.report()
{'f': 0, 'g': 7, 'H': 0, 'Hprod': 0, 'tsetup': 0.0, 'trun': 0.0, 'c': None, 'cg': None, 'cH': None}
0.000000 7.812500 0.000000 0.000000 0.000000 0.000000 0.000000 >>> p.report()
{'f': 0, 'g': 8, 'H': 0, 'Hprod': 0, 'tsetup': 0.0, 'trun': 0.0, 'c': None, 'cg': None, 'cH': None}
0.000000 8.500000 0.000000 0.000000 0.000000 0.000000 0.000000 >>> 

The intermediate prints are the actual values of calls as returned by the C interface.

Why does this only happen on macOS? What is going on here?

[jfowkes]

Moved to issue #86