Follow-up from "Hide keyboard shortcuts in tooltips when disabled"

The following discussion from !143067 (merged) should be addressed:

• @lorenzvanherwaarden started a discussion:

  I do think we should add some test coverage though (unless we have some exceptions for testing tooltips).

Implementation plan

1. For header_actions.vue, sidebar_assignees_widget.vue, labels_select_root.vue:
   1. check the value we're passing for the tooltip, shortcut description and shortcut key
   2. also check these when shouldDisableShortcuts() === true
2. For web_ide_link.vue, check that we're adding a <kbd /> with the shortcut content in it if the action has a shortcut, and that it's not added when shouldDisableShortcuts() === true (even though it has a shortcut).