[web] fix css file generation permission bug (closes #17143773) PropertySheet.process_resource() uses mkstemp which enforce a 0600 mode on the output file, which is not the file permission we want for css files.

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