add a bit more test checks

Author: brhx

packages/start-client-core/src/tests/createServerFn.test-d.ts

@@ -5,6 +5,7 @@ import { TSS_SERVER_FUNCTION } from '../constants'
 import type {
   Constrain,
   Register,
+  ValidateSerializableInput,
   TsrSerializable,
   Validator,
 } from '@tanstack/router-core'
@@ -311,7 +312,10 @@ test('createServerFn returns Date', () => {
     dates: [new Date(), new Date()] as const,
   }))
 
-  expectTypeOf(fn()).toEqualTypeOf<Promise<{ dates: readonly [Date, Date] }>>()
+  expectTypeOf<ReturnType<typeof fn>>().toMatchTypeOf<Promise<unknown>>()
+  expectTypeOf<Awaited<ReturnType<typeof fn>>>().toMatchTypeOf<
+    ValidateSerializableInput<Register, { dates: readonly [Date, Date] }>
+  >()
 })
 
 test('createServerFn returns undefined', () => {