docs: update guide to use vitest 3

Author: edmundhung

src/content/docs/agents/getting-started/testing-your-agent.mdx

@@ -23,7 +23,7 @@ The `agents-sdk-starter` template and new Cloudflare Workers projects already in
 Before you write your first test, install the necessary packages:
 
 ```sh
-npm install vitest@2.1.8 --save-dev --save-exact
+npm install vitest@~3.0.0 --save-dev --save-exact
 npm install @cloudflare/vitest-pool-workers --save-dev
 ```
 

src/content/docs/workers/testing/vitest-integration/get-started/migrate-from-miniflare-2.mdx

@@ -30,7 +30,7 @@ First, you will need to uninstall the old environment and install the new pool.
 
 ```sh
 npm uninstall vitest-environment-miniflare
-npm install --save-dev --save-exact vitest@2.1.8
+npm install --save-dev --save-exact vitest@~3.0.0
 npm install --save-dev @cloudflare/vitest-pool-workers
 ```
 

src/content/docs/workers/testing/vitest-integration/get-started/write-your-first-test.mdx

@@ -24,15 +24,15 @@ This guide will instruct you through installing and setting up the `@cloudflare/
 Open a terminal window and make sure you are in your project's root directory. Once you have confirmed that, run:
 
 ```sh
-npm install vitest@2.1.8 --save-dev --save-exact
+npm install vitest@~3.0.0 --save-dev --save-exact
 npm install @cloudflare/vitest-pool-workers --save-dev
 ```
 
 The above commands will add the packages to your `package.json` file and install them as dev dependencies.
 
 :::note
 
-Currently, the `@cloudflare/vitest-pool-workers` package _only_ works with Vitest 2.0.x - 2.1.8.
+Currently, the `@cloudflare/vitest-pool-workers` package _only_ works with Vitest 2.0.x - 3.0.x.
 
 :::