Type Error onServerValidate async

[CoachNooB]

Describe the bug

I got red squigly line when putting async in onServerValidate. But it run normally in runtime.
Type Promise <string | undefined> is not assignable to type ValidationError

Your minimal, reproducible example

https://www.typescriptlang.org/play/?#code/PTAEHUFMBsGMHsC2lQBd5oBYoCoE8AHSAZVgCcBLA1UABWgEM8BzM+AVwDsATAGiwoBnUENANQAd0gAjQRVSQAUCEmYKsTKGYUAbpGF4OY0BoadYKdJMoL+gzAzIoz3UNEiPOofEVKVqAHSKymAAmkYI7NCuqGqcANag8ABmIjQUXrFOKBJMggBcISGgoAC0oACCbvCwDKgU8JkY7p7ehCTkVDQS2E6gnPCxGcwmZqDSTgzxxWWVoASMFmgYkAAeRJTInN3ymj4d-jSCeNsMq-wuoPaOltigAKoASgAywhK7SbGQZIIz5VWCFzSeCrZagNYbChbHaxUDcCjJZLfSDbExIAgUdxkUBIursJzCFJtXydaiKKEEeBkGgAb1A7EEkAAYlTEKAAL44thsgBEAAFUGZBILYPFgJNYKhSslWTyANzBBCcYU41mgAC89MZLLIiAAFDTFCUStxIMkGFFUAA1BjQdiQfKgQ3Gl39BjIR08nlG43s3jBF2NYjfPRkG3QCjcOoOsTHcygA2gHS2+0cgCUGoAfE6fa7QCoACIYCpx2CgYNkUOgcORuoNTi5jmKdlp4IqHDNDxkLyIKnOYHsGhfNxmZjsBjMSD8WAR0ViYF6EReHkAUVW7oW+h5SWxPPADlQAHJhAA5SASHlBFQAeS+ZHejP4k6OgupkFc0jwoCcvZ0wyw+goAgiDQsIlzDhIVLRCIBgcNiCxMKwHA8EEihAA

Steps to reproduce

1. Put async in the onServerValidate
2. Got Type error

Expected behavior

No Type Error.

How often does this bug happen?

Every time

Screenshots or Videos

Platform

• OS: Windows
• Browser: OperaGX

TanStack Form adapter

react-form

TanStack Form version

v0.20.2

TypeScript version

v5.4.2

Additional context

No response

[my-slab]

I had a crack at fixing it in #822.

[Balastrong]

Implemented in #855