Fix accessibility violations in List Storybook

[navedqb]

What does this PR do?

Fixes accessibility violations in 2 List storybooks

Where should the reviewer start?

List component storybooks

What testing has been done on this PR?

How should this be manually tested?

• List/Pinned
• List/Order

Do Jest tests follow these best practices?

• screen is used for querying.
• The correct query is used. (Refer to this list of queries)
• userEvent is used in place of fireEvent.
• asFragment() is used for snapshot testing.

Any background context you want to provide?

What are the relevant issues?

#6124

Screenshots (if appropriate)

Do the grommet docs need to be updated?

Should this PR be mentioned in the release notes?

Is this change backwards compatible or is it a breaking change?

[jcfilben]

It looks like when List has onClickItem or onOrder defined the role of the list component is set to 'listbox' I think we should always have role='list' regardless of onClickItem or onOrder. I think we can make this change in the List.js file (see line 222).

[jcfilben]

It looks like some of the List tests are failing because they are trying to reference the 'listbox' role. We should change those tests to use screen.getByRole('list') (See List/__tests__/List-test.js).

The test snapshots will also need updated. To do this you can run yarn jest -u.