Cypress tests for partial page load

[osma]

Description of the enhancement

Add Cypress tests for the already existing partial page load functionality. The sidebar components (alphabetical, hierarchy) already support this (clicking on concepts in either of these performs a partial page load of the concept information) but current Cypress test do not verify that all functionality is working after partial page loads.

Initial TODO:

• Ensure that there are Cypress tests for partial page loads in all situations where this happens (all page types that show a sidebar)
• The old draft PR Add cypress tests for partial page load on vocab home page #1474 by @UnniKohonen contains proposed Cypress tests for partial page load; see if it can be reused, or close it if it cannot.
• Adjust the Cypress tests for the concept page; make sure they verify functionality both with and without partial page loads (perhaps using dynamic tests; each test should be executed twice - with and without partial page load)

Who are the users that would benefit from the enhancement and how?

Skosmos developers. It's easy to forget testing after partial page loads.

What new functionalities would the enhancement make possible?

Ensure that functionality is not broken by accident.

Why is the enhancement important?

Breakage after partial page loads has happened several times in recent development sprints, so the problem is urgent.