Update CHANGELOG.md for v8.4.2 [skip ci]

CHANGELOG.md

@@ -1,3 +1,11 @@
+## 8.4.2
+
+- Addon Test: Fix post-install logic for Next.js Vite framework support - [#29524](https://github.com/storybookjs/storybook/pull/29524), thanks @valentinpalkovic!
+- Addon Test: Only render the TestingModule component in development mode - [#29501](https://github.com/storybookjs/storybook/pull/29501), thanks @yannbf!
+- CLI: Fix Solid init by installing `@storybook/test` - [#29514](https://github.com/storybookjs/storybook/pull/29514), thanks @shilman!
+- Core: Shim CJS-only globals in ESM output - [#29157](https://github.com/storybookjs/storybook/pull/29157), thanks @valentinpalkovic!
+- Next.js: Fix bundled react and react-dom in monorepos - [#29444](https://github.com/storybookjs/storybook/pull/29444), thanks @sentience!
+
 ## 8.4.1
 
 - Core: Relax peer dep constraint of shim packages - [#29503](https://github.com/storybookjs/storybook/pull/29503), thanks @kasperpeulen!