[WNMGDS-3315] Fixed aria-invalid property previously assigned to Dropdown Button

[kim-cmsds]

Summary

• Aria recommendations in version 1.2 have changed from applying the aria-invalid value to any kind of element to a specific list of elements based on role (source).
• The dropdown component (storybook link) had been applying the aria-invalid role to the Dropdown Button, which is no longer a valid element of which to apply that attribute.
• This PR applies the aria-invalid attribute to the element with the listbox role instead, which is an allowed role for that attribute.
• Jira ticket
• Note: this ticket includes steps to reproduce on the production storybook instance, which might help illustrate the issue for reviewers

How to test

1. Run storybook locally npm run storybook and go to the Dropdown
2. Inspect the dropdown example's source, and notice how the <button> element no longer has aria-invalid="false"
3. Close the inspector, and run the Siteimprove browser extension
4. Ensures that Siteimprove no longer reports the error, "ARIA attribute unsupported or prohibited"

Checklist

• Prefixed the PR title with the Jira ticket number as [WNMGDS-####] Title or [NO-TICKET] if this is unticketed work.
• Selected appropriate Type (only one) label for this PR, if it is a breaking change, label should only be Type: Breaking
• Selected appropriate Impacts, multiple can be selected.
• Selected appropriate release milestone

If this is a change to code:

• Created or updated unit tests to cover any new or modified code
• Verified that running both npm run test:unit and npm run test:browser:all were each successful
• If necessary, updated unit-test snapshots (npm run test:unit:update) and browser-test snapshots (npm run test:browser:all:update)

[tamara-corbalt]

Looks good to me!

[jack-ryan-nava-pbc]

Looks great! Well done