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.

vite-embedded.config.ts

@@ -8,7 +8,7 @@ Please see LICENSE in the repository root for full details.
 import { defineConfig, mergeConfig } from "vite";
 import generateFile from "vite-plugin-generate-file";
 
-import fullConfig from "./vite.config";
+import fullConfig from "./vite.config.ts";
 
 const base = "./";