Fix failing 'test_double_conversion' test
Fix failing 'test_double_conversion' test

Fix incorrect part of 'test_double_conversion' test in test_conversion.py.
An 'OverflowError' was expected for valid values, which represent Python
'inf' and '-inf'.
The problem was identified with support of conversion for Python 'inf'
and '-inf' to .NET System.Double PositiveInfinity and NegativeInfinity.

See also: #487.

Konstantin-Posudevskiy/pythonnet,Konstantin-Posudevskiy/pythonnet,Konstantin-Posudevskiy/pythonnet