Python 2: %s formatting a greenlet results in a unicode object instead of a str

[jamadden]

Because tp_repr is using PyUnicode_Format; directly calling repr or str converts the result to a str, but for some reason %s formatting does not.

>>> import sys
>>> print(sys.version)
2.7.18 (default, Sep  7 2020, 05:51:03)
[GCC Apple LLVM 12.0.0 (clang-1200.0.31.1)]
None
>>> import greenlet
>>> '%s' % (greenlet.getcurrent(),)
u'<greenlet.greenlet object at 0x10694b910 (otid=0x106bd1950) current active started main>'