Fixed flawed example code for Accordion (#2853)

* Fixed flawed example code

Fixed an issue with the example code for accordion.

The flawed code:
- Rendered a read-only field due to checked being set to a value instead of using "defaultChecked".
- Raised an error in TypeScript (TS2322: Type `string` is not assignable to type `boolean | undefined`)

This addresses both those issues

* Added replacement string

* - Reverted changes

src/docs/src/lib/actions.js

@@ -31,6 +31,7 @@ export function htmlToJsx(node) {
     '"0"': "{0}",
     "<!--": "{/*",
     "-->": "*/}",
+    'checked="checked"': "defaultChecked",
 
     // "accent-height=": "accentHeight=",
     // "alignment-baseline=": "alignmentBaseline=",