[ic-page-header] storybook accessibility plug in complaining of two elements with role="banner"

[GCHQ-Developer-530]

Summary of the bug

On storybook examples of page header with top nav, the built in storybook accessibility plug in is failing due to two elements having a banner role and all roles should be unique.

🪜 How to reproduce

Tell us the steps to reproduce the problem:

1. Go to page-header sticky-with-content-and-footer example
2. Click on accessibility plug in in the drawer
3. See the error

alternatively the error can be replicated on our https://design.sis.gov.uk/top-navigation-page-header-pattern/
If you do a full page scan using the 'axe Dev Tools' browser plugin, it appears as a moderate issue.
If you do an Accessibility Assessment using the IBM Equal Access Accessibility Checker it also appears.

📸 Screenshots or code

🧐 Expected behaviour

It should only have one banner.

Additional info

Weirdly page header doesn't have a banner role. This doesn't fail accessibility insights fast pass either so it's hard to tell if it's a weird quirk of storybook or not.

[gd2910]

Investigate ways around this, consider https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/presentation_role

Or conditional role on IcPageHeader when in conjunction with IcTopNavigation

[gd2910]

Test IcTopnavigation and IcPageHeader layout patterns to recreate issue.

[MI6-255]

Take banner off Page Header and find a role to replace it