USWDS-Site: Resolve pa11y and html-proofer errors

[amyleadem]

Summary

Resolved a couple of errors that appeared in html-proofer and after the test upgrade to pa11y-ci v3.0 (This upgrade has not been included in this PR).

Related issue

Closes #1860

Preview link

Preview links:

• Data Visualizations - Bar charts
• What's New

Problem statement

Tests to upgrade to pa11y-ci 3 revealed a new valid aria error:

html-proofer returned the error:

For the Links > External check, the following failures were found:
* At ./_site/about/whats-new/index.html:2440:
 External link https://github.com/uswds/uswds-assets/issues/new failed (status code 404)
HTML-Proofer found 1 failure!

Solution

• On Data Visualizations page, connected aria-describedby to the appropriate related id.
• On What's new page, updated a broken link.

Testing and review

Confirm that the updated items continue to work as expected and that tests complete without error.

[mejiaj]

Thanks for those specific preview links, very helpful!