[server/sources] fix name error in eid_type_source_pre_131 i.e. the eid_type_source implementation used when some pre 3.13.1 database is detected. Regression from 5fbdbbe51867.

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
http://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))