[sql gen] Properly create UNIQUE index on non string column. Closes #13728492 Unique was previously detected in a loop triggered only for String columns.

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