chore: ignore TS error in config object

Fixes #2483

The introduction of `idPrefix` in Vue's `AppConfig` object triggers a TS error that we can't really get rid of (see #2483 for a more detailled explanation).

src/createInstance.ts

@@ -260,6 +260,7 @@ export function createInstance(
       keyof Omit<AppConfig, 'isNativeTag'>,
       any
     ][]) {
+      // @ts-expect-error https://github.com/vuejs/test-utils/issues/2483
       app.config[k] = isObject(app.config[k])
         ? Object.assign(app.config[k]!, v)
         : v