[Columns/Box] Add missing children prop back to prop type (#7483)

### WHY are these changes introduced?

The `children` prop must have been accidentally deleted in a previous PR
so adding it back.

### WHAT is this pull request doing?

Adds `children` as optional prop to `ColumnsProps`.
Also runs `get-props` script in styleguide so props are updated.

<!-- ℹ️ Delete the following for small / trivial changes -->

### How to 🎩

🖥 [Local development
instructions](https://github.com/Shopify/polaris/blob/main/README.md#local-development)
🗒 [General tophatting
guidelines](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting.md)
📄 [Changelog
guidelines](https://github.com/Shopify/polaris/blob/main/.github/CONTRIBUTING.md#changelog)

### 🎩 checklist

- [ ] Tested on
[mobile](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting.md#cross-browser-testing)
- [ ] Tested on [multiple
browsers](https://help.shopify.com/en/manual/shopify-admin/supported-browsers)
- [ ] Tested for
[accessibility](https://github.com/Shopify/polaris/blob/main/documentation/Accessibility%20testing.md)
- [ ] Updated the component's `README.md` with documentation changes
- [x] [Tophatted
documentation](https://github.com/Shopify/polaris/blob/main/documentation/Tophatting%20documentation.md)
changes in the style guide

Author: laurkim

.changeset/large-peas-happen.md

@@ -0,0 +1,6 @@
+---
+'@shopify/polaris': patch
+'polaris.shopify.com': patch
+---
+
+Fixed missing `children` prop in `Columns` prop type

polaris-react/src/components/Columns/Columns.tsx

@@ -23,6 +23,7 @@ export interface ColumnsProps extends PropsWithChildren {
    * @default {xs: 6, sm: 6, md: 6, lg: 6, xl: 6}
    */
   columns?: Columns;
+  children?: React.ReactNode;
 }
 
 export function Columns({columns, children, spacing}: ColumnsProps) {