Use with fluent-json-schema now requires to call valueOf in ObjectSchema when using Typescript

### Prerequisites

- [X] I have written a descriptive issue title
- [X] I have searched existing issues to ensure the regression has not already been reported

### Last working version

5.1.0

### Stopped working in version

5.1.1

### Node.js version

18.x

### Operating system

macOS

### Operating system version (i.e. 20.04, 11.3, 10)

12.3

### 💥 Regression Report

Typings in Typescript now throw an error when using a `fluent-json-schema` generated schema as input for `envSchema`

### Steps to Reproduce

In a Typescript file the next block of code reproduces the issue

```ts
import envSchema from 'env-schema'
import S from 'fluent-json-schema'

envSchema({
schema: S.object()
})
```

```
Type 'ObjectSchema' is not assignable to type 'AnySchema | UncheckedJSONSchemaType | undefined'.
Type 'ObjectSchema' is not assignable to type '{ type: "object"; additionalProperties?: boolean | UncheckedJSONSchemaType | undefined; unevaluatedProperties?: boolean | UncheckedJSONSchemaType | undefined; ... 7 more ...; maxProperties?: number | undefined; } & { ...; } & { ...; } & { ...; }'.
Property 'type' is missing in type 'ObjectSchema' but required in type '{ type: "object"; additionalProperties?: boolean | UncheckedJSONSchemaType | undefined; unevaluatedProperties?: boolean | UncheckedJSONSchemaType | undefined; ... 7 more ...; maxProperties?: number | undefined; }'.ts(2322)
```

Nevertheless the following block of code does not throw an error

```ts
import envSchema from 'env-schema'
import S from 'fluent-json-schema'

envSchema({
schema: S.object().valueOf
})
```

### Expected Behavior

As `ObjectSchema` from `fluent-json-schema` was removed from typings in #137 it might be solved otherwise or maybe be documented to avoid future confusion