Invalid Key for User Relation in Strapi 5.8.1
### Node Version

18.20.6

### NPM/Yarn/PNPM Version

10.8.2

### Strapi Version

5.8.1

### Operating System

Windows 11

### Database

PostgreSQL

### Javascript or Typescript

Javascript

### Reproduction URL

_No response_

### Bug Description

I'm facing an issue when trying to create a user profile via the API in Strapi (version 5.8.1). The relation between the UserProfile and User models is correctly set up, but I keep getting the error Invalid key user or Invalid relations when sending the request.

I’ve tried sending the user ID as part of the data for the relation, but Strapi keeps returning the error saying the user key is invalid.

### Steps to Reproduce

1. UserProfile and User models are related with a oneToOne relation:

```
"user": {
  "type": "relation",
  "relation": "oneToOne",
  "target": "plugin::users-permissions.user"
}
```

2. I send the following request payload when creating a new user profile:

```
{
  "data": {
    "profilePicture": "url-obrazku",
    "bio": "Test bio",
    "socialLinks": [],
    "location": "Some location",
    "birthday": "2025-02-12",
    "experiencePoints": 1,
    "user": 23,
    "badges": []
  }
}
```
3. Response: I receive a 400 Bad Request with the following error:

```
{
  "data": null,
  "error": {
    "details": {
      "key": "user",
      "path": "user",
      "source": "body"
    },
    "message": "Invalid key user",
    "name": "ValidationError",
    "status": 400
  }
}

```

### Expected Behavior

- The user profile should be created successfully with the correct relation to the User model.
- The user relation key should be accepted, and the UserProfile should be properly populated with the User ID.

### Logs

```shell

```

### Code Snippets

Model configuration for UserProfile:

    "user": {
      "type": "relation",
      "relation": "oneToOne",
      "target": "plugin::users-permissions.user"
    }

### Media

_No response_

### Additional information

_No response_

### Confirmation Checklist

- [x] I have checked the existing [issues](https://github.com/strapi/strapi/issues) for duplicates.
- [x] I agree to follow this project's [Code of Conduct](https://github.com/strapi/strapi/blob/develop/CODE_OF_CONDUCT.md).