devel/py-meliae: limit supported python versions

meliae/_scanner.c:3388:46: error: use of undeclared identifier 'PyGC_Head'

__pyx_t_1 = __Pyx_PyInt_FromSize_t((sizeof(PyGC_Head))); if (unlikely(!__pyx_t_1)) __PYX_ERR(0, 52, __pyx_L1_error)

Approved by: portmgr blanket