Ignoring cython==0.29.31

[tombo315]

Related issue: https://github.com/cython/cython/issues/4927

pip install python-pkcs11

Results in:

pkcs11/_pkcs11.c:45689:20: error: lvalue required as left operand of assignment
    45689 |     CYTHON_ATOMICS = __Pyx_PyObject_IsTrue(o); if (unlikely((CYTHON_ATOMICS == (int)-1) && PyErr_Occurred())) __PYX_ERR(3, 26, __pyx_L2_error)
          |                    ^
    error: command 'gcc' failed with exit status 1

Other work-around is to:

pip install cython==0.29.30
pip install python-pkcs11