fix: ensure tab label and description are serializable (#10115)

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### What?

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Fixes #

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### What?
This PR fixes an issue where assigning a label or description function
to a tab would cause a runtime error due to passing a function to a
client component.

### Why?
To prevent runtime errors when using non-static designations.

### How?
By properly evaluating label and description functions prior to
assignment to their `clientTab` counterpart.

Fixes #10114

Before:

![image](https://github.com/user-attachments/assets/e003780a-2f24-4988-96ce-27c22fd61854)

After:

![image](https://github.com/user-attachments/assets/0bd185a0-415d-4414-bead-48647e244ba7)

test/_community/payload-types.ts

@@ -336,4 +336,4 @@ export interface Auth {
 declare module 'payload' {
   // @ts-ignore 
   export interface GeneratedTypes extends Config {}
-}
+}