Directive on Input Type Receives Map instead of Object

### What happened?

I wanted to implement a custom directive for `input` types called `@validate`.

My directive hook looks like this:

```go
config.Directives.Validate = func(ctx context.Context, obj interface{}, next graphql.Resolver) (res interface{}, err error) {
if _, ok := obj.(map[string]any); ok {
return next(ctx)
}

if err := validate.StructCtx(ctx, obj); err != nil {
return nil, err
}

return next(ctx)
}
```

### What did you expect?

I expected the `validate.StructCtx` to be called, and `obj` to be of the type `model.CreateCarInput`.

### Minimal graphql.schema and models to reproduce

```gql
directive @validate on OBJECT | INPUT_OBJECT

input CreateCarInput @validate {
make: String! @goTag(key: "validate", value: "notblank")
model: String!
type: String!
year: Int!
}
```

### versions
- `go run github.com/99designs/gqlgen version` v0.17.49
- `go version` go version go1.22.3 linux/amd64