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).

some conversion (TextDocument) depend on the content type, so it's
necessary to first update the content type before trying to convert to
base format