[test] fix test_printable_value_bytes with current pygments
An empty span was added in
https://bitbucket.org/birkenfeld/pygments-main/commits/164574c13533195a555181a2b9c685fea2470403
(grafted from 74b04a88d28a)
usr/lib/python2*/*-packages/cubicweb/web
usr/lib/python2*/*-packages/cubicweb/wsgi
usr/share/cubicweb/cubes/shared/data
usr/share/cubicweb/cubes/shared/wdoc