docs: Update playground links for v2 in the v2 doccumentation (#8902)

Author: nvh95

CONTRIBUTING.md

@@ -99,7 +99,7 @@ Note: The test build environment uses a [different default set of Vite config](h
 
 ### Extending the Test Suite
 
-To add new tests, you should find a related playground to the fix or feature (or create a new one). As an example, static assets loading are tested in the [assets playground](https://github.com/vitejs/vite/tree/main/packages/playground/assets). In this Vite App, there is a test for `?raw` imports, with [a section is defined in the `index.html` for it](https://github.com/vitejs/vite/blob/71215533ac60e8ff566dc3467feabfc2c71a01e2/packages/playground/assets/index.html#L121):
+To add new tests, you should find a related playground to the fix or feature (or create a new one). As an example, static assets loading are tested in the [assets playground](https://github.com/vitejs/vite/tree/v2/packages/playground/assets). In this Vite App, there is a test for `?raw` imports, with [a section is defined in the `index.html` for it](https://github.com/vitejs/vite/blob/71215533ac60e8ff566dc3467feabfc2c71a01e2/packages/playground/assets/index.html#L121):
 
 ```html
 <h2>?raw import</h2>

docs/guide/ssr.md

@@ -22,8 +22,8 @@ If you have questions, the community is usually helpful at [Vite Discord's #ssr
 
 Vite provides built-in support for server-side rendering (SSR). The Vite playground contains example SSR setups for Vue 3 and React, which can be used as references for this guide:
 
-- [Vue 3](https://github.com/vitejs/vite/tree/main/packages/playground/ssr-vue)
-- [React](https://github.com/vitejs/vite/tree/main/packages/playground/ssr-react)
+- [Vue 3](https://github.com/vitejs/vite/tree/v2/packages/playground/ssr-vue)
+- [React](https://github.com/vitejs/vite/tree/v2/packages/playground/ssr-react)
 
 ## Source Structure
 
@@ -177,7 +177,7 @@ Then, in `server.js` we need to add some production specific logic by checking `
 
 - Move the creation and all usage of the `vite` dev server behind dev-only conditional branches, then add static file serving middlewares to serve files from `dist/client`.
 
-Refer to the [Vue](https://github.com/vitejs/vite/tree/main/packages/playground/ssr-vue) and [React](https://github.com/vitejs/vite/tree/main/packages/playground/ssr-react) demos for working setup.
+Refer to the [Vue](https://github.com/vitejs/vite/tree/v2/packages/playground/ssr-vue) and [React](https://github.com/vitejs/vite/tree/v2/packages/playground/ssr-react) demos for working setup.
 
 ## Generating Preload Directives