docs: Icon overview doesn't get displayed correctly

[mfranzke]

The possibility to choose an icon isn't working any more in newer versions higher than 0.28.0: https://db-ui.github.io/elements/version/v0.28.0/?path=/story/db-icon--live-demo&args=icon:arrow-up;variant:16-outline

Compare to https://db-ui.github.io/elements/?path=/story/db-icon--live-demo&args=icon:arrow-up;variant:16-outline

This is probably related to the Storybook 7 update with #2093

the version 0.28.0 even already had the following output:

329.24b058d6.iframe.bundle.js:2 `argType.defaultValue` is deprecated and will be removed in Storybook 7.0.

https://github.com/storybookjs/storybook/blob/next/MIGRATION.md#no-longer-inferring-default-values-of-args