If preferences are not set, this causes a non existant style to be used

On recent pylint, this is flagged as unnecessary-pass

Also update the link that was pointing to python2 doc

We want these columns to be "binary" so that mariadbd compares them
without any collation, but we don't want to use binary type, because on
python 3 the brain attributes are bytes (user ids are strings everywhere
else).

This also normalize the same columns present in worklist cache table.

I don't know a PYTHONHASHSEED to see the problem on python2, but on
python 3 erp5_payroll_l10n_fr:testSimplifiedPayslipReport fails all the
time with this.

On python3 the percentages are sometimes printed as 6.8500000000000005%

it was using bytes, but this seems wrong now that we did 31af8997
(XMLExportImport: Base_asXML and Folder_asXML return str, not bytes.,
2024-03-07).

use Image portal type to store image data. Using a Web Page never made
sense, it was working on python2 because the lax difference between
between text and bytes.

This test a svg contained in various portal types (Image, Web Page, )
with a png background image. The problem was with the background image.
This change does not affect the portal type containing the svg, only
the png background image.