gh-98608: Stop Treating All Errors from _Py_NewInterpreterFromConfig() as Fatal (gh-102657)

Prior to this change, errors in _Py_NewInterpreterFromConfig() were always fatal.  Instead, callers should be able to handle such errors and keep going.  That's what this change supports.  (This was an oversight in the original implementation of _Py_NewInterpreterFromConfig().)  Note that the existing [fatal] behavior of the public Py_NewInterpreter() is preserved.

https://github.com/python/cpython/issues/98608