chore(eslint-config): fix type error in vitest config

This commit addresses a TypeScript error in the vitest configuration file within the eslint-config package. The `vitestPlugin.configs.recommended` is now explicitly cast to `Linter.Config` to resolve the type mismatch. A comment has been added to explain that the `configs` property is loosely typed, necessitating this workaround.

packages/eslint-config/configs/vitest.ts

@@ -3,7 +3,8 @@ import vitestPlugin from '@vitest/eslint-plugin'
 
 export function vitest(): Linter.Config[] {
   return [
-    vitestPlugin.configs.recommended,
+    // @ts-expect-error: the `configs` property is loosely typed.
+    vitestPlugin.configs.recommended as Linter.Config,
     {
       rules: {