[Storybook] Disabled component are still focusable in Firefox

[ciampo]

Description

This is likely a regression introduced by #44865, which causes the Disabled component to rely on the inert attribute.

The inert attribute is not supported by Firefox browsers, and the polyfill doesn't seem to work in preventing elements wrapped in Disabled from being keyboard-focusable.

What needs to be clarified is whether the polyfill is loaded at all in Storybook — depending on that, this may be either an environment-specific issue, or a Gutenberg-wide problem

Step-by-step reproduction instructions

1. Visit https://wordpress.github.io/gutenberg/?path=/story/components-disabled--default using the firefox browser
2. Make sure the isDisabled is set to true
3. With the keyboard, focus the different input fields

Screenshots, screen recording, code snippet

Kapture.2022-10-24.at.20.32.27.mp4

Environment info

Firefox, MacOS

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[youknowriad]

I confirmed that there's no regression in Firefox, it's just that there's no polyfill (not just the inert one) is actually loaded in storybook.

[ciampo]

Thank you for the confirmation, Riad! I'm going to change the PR's description to better reflect that the issue is only in Storybook.