fix: vitest merge config in form of callback

[DingYuanhao]

I got an vitest error using create-vue template:

Error: Vitest failed to start:
Error: Cannot merge config in form of callback
at mergeConfig (file://...)

Fixed it according to vitest's official documentation

[haoqunjiang]

But our vite config isn't defined as an function. Would you please open an issue with a runnable reproduction?

[DingYuanhao]

But our vite config isn't defined as an function. Would you please open an issue with a runnable reproduction?

Sorry, my mistake 😅 The issue lies with my vite.config.ts file, where I defined the Vite config in a functional way. I thought that defining the Vite config as mentioned in the PR would make it more universal. However, in this case, if it is not defined as a function, a new TypeScript error would be raised, even though Vitest runs successfully. Feel free to close the PR anyway :)