Bug#945411: pyfai fails tests with Python 3.8

[Drew Parsons]

Package: pyfai
Version: 0.18.0+dfsg1-3
Followup-For: Bug #945411

"pocl error: lt_dlopen("(null)") or lt_dlsym() failed with 'can't close 
resident module'"

That suggests pocl is not yet built against python3.8