The Documents app test suite was adjusted to stay aligned with recent platform changes. This helps keep automated quality checks reliable without changing the user experience.

This commit adapts a test with regard to changes made in https://github.com/odoo/odoo/pull/126041.

task-3258625

The Documents PDF splitter now lets users use Shift+A to clear all selected pages when every page is already selected. This makes bulk page selection faster and more intuitive when organizing or splitting PDFs.

This commit makes so that in addition to selecting all pages with
'shift-A', it will unselect all pages if they are all already selected.

task-2429945