The PyObject structure is part of the stable ABI, but PyGC_Head is not.
https://www.python.org/dev/peps/pep-0384/#structures
I can understand that it's annoying to not be able to use the same wheel package on Python 3.7 <= 3.7.4 and Python Python 3.7 >= 3.7.5, but I don't think that we can fix this issue.
I suggest to close it as "rejected".
One solution is to require to build your C extension on installation (don't ship wheel packages).
If you want to ship wheel package, another compromise would be to require Python 3.7.5 or newer, and check early the Python version.