Federation error `federation and exec must be in the same package`

### What happened?
Trying to configure federation but found this error

```sh
failed to load schema: federation and exec must be in the same package
exit status 1
make: *** [generate] Error 1
```

#### gqlgen.yml
```yml
schema:
- schemas/*.graphqls

exec:
dir: internal/infra/graph/generated
package: generated

federation:
filename: internal/infra/graph/generated/federation.go
package: generated
version: 2

model:
filename: internal/infra/graph/model/models_gen.go
package: model

resolver:
layout: follow-schema
dir: internal/infra/resolvers
package: resolvers
filename_template: "{name}_resolver.go"

models:
ID:
model:
- github.com/99designs/gqlgen/graphql.ID
- github.com/99designs/gqlgen/graphql.Int
- github.com/99designs/gqlgen/graphql.Int64
- github.com/99designs/gqlgen/graphql.Int32
Int:
model:
- github.com/99designs/gqlgen/graphql.Int
- github.com/99designs/gqlgen/graphql.Int64
- github.com/99designs/gqlgen/graphql.Int32
UUID:
model:
- github.com/99designs/gqlgen/graphql.UUID

```

### What did you expect?
The generate should work as expected and it generates the federated content in `federation.go`

### Minimal graphql.schema and models to reproduce
```graphql
type Product @key(fields: "id") {
id: ID!
name: String!
}

type Query {
products: [Product!]!
}

```

### versions
- `go run github.com/99designs/gqlgen version`? - `v0.17.47`
- `go version`? - `1.20`

> Without federation config on `gqlgen.yml`, `generate` is working as expected