fix: typo of numbering (#1306)

Author: snjro

docs/svelte-testing-library/setup.mdx

@@ -64,13 +64,13 @@ npm install --save-dev @vitest/ui
 4. Optionally install [vitest-dom](https://github.com/chaance/vitest-dom) to add
    handy assertions to Vitest
 
-   5.1 Install `vitest-dom`
+   4.1 Install `vitest-dom`
 
    ```bash npm2yarn
    npm install --save-dev vitest-dom
    ```
 
-   5.2 import `vitest-dom` at within the vitest setup file (usually `vitest-setup.(js|ts)`)
+   4.2 import `vitest-dom` at within the vitest setup file (usually `vitest-setup.(js|ts)`)
 
    ```js
     import * as matchers from "vitest-dom/matchers";