Enable Axe tests for global and vocab search result pages

[osma]

Description of the enhancement

Currently we have Cypress Axe accessibility tests for most page types, but the tests for global and vocab search pages are disabled (probably because search result pages were not yet implemented at the time):

• https://github.com/NatLibFi/Skosmos/blob/main/tests/cypress/accessibility/axe-global-search.cy.js
• https://github.com/NatLibFi/Skosmos/blob/main/tests/cypress/accessibility/axe-vocab-search.cy.js

We should enable the Axe tests for these page types and ensure that the tests pass.

Related issues (known accessibility problems on the search result pages):

• [Accessibility], WCAG 1.3.1. Groupings of search results are not conveyed to screen readers #1975
• [Accessibility], WCAG 1.1.1 The icons on the Search Results page do not have alt texts and they are uncler to many users #1967

If Axe detects these, then they need to be fixed before we can enable the Axe tests in CI.

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

Any users, especially those who need accessibility features

What new functionalities would the enhancement make possible?

Test that no accessibility issues (those covered by Axe) are mistakenly introduced on search result pages.

Why is the enhancement important?

Accessibility is important. Automated testing is important.