Fix Vitest import warning

Fixes the following warning:

[warn] (!) Your Vite config uses features that are unsupported by `configLoader: 'native'`, which is planned to become the default in a future major version of Vite:
  - import "./vite.config" without a file extension (vitest.config.ts:3:35). Add the file extension
Set `VITE_CONFIG_NATIVE_IGNORE_WARNING=true` to suppress this warning.

vitest.config.ts

@@ -1,6 +1,6 @@
 import { defineConfig, mergeConfig } from "vitest/config";
 import { playwright } from "@vitest/browser-playwright";
-import { vitePluginsConfig } from "./vite.config";
+import { vitePluginsConfig } from "./vite.config.ts";
 import { storybookTest } from "@storybook/addon-vitest/vitest-plugin";
 import path from "node:path";
 import { fileURLToPath } from "node:url";