WCAG violations in Cypress testing

### Description of the bug

After #1267, there are now multiple known WCAG violations, all noted down in `test/e2e/support/custom.ts`. When these get fixes, they should be removed from the list, and at some point we can set `skipFailures = false` again.

### Steps To Reproduce

1. Try setting `skipFailures = true` in `custom.ts`, or comment out the entry for each known violation
2. Watch all the tests mentioned in the list of known violations fail

### Additional Information

If you comment out entries in `knownWcagViolations` and run each test, you'll get a link to a help page where you can investigate what needs to be done to fix the problem. Also, if you click on the error in the Cypress log, you can inspect which nodes/elements were found to be in violation.

Start with test/e2e/support/custom.ts and the knownWcagViolations list. Comment out each entry, run the corresponding Cypress test, and use its help-page link and Cypress log to inspect the violating elements. Done means fixing the violations, removing their entries, and eventually restoring skipFailures = false.

Written by the indexing model from the issue text.