GraphQL Interface With GqlGen

### What happened?
I'm trying to implement the GraphQL Interface but it's not working. I'm getting following error:
```{
"errors": [
{
"message": "json: cannot unmarshal object into Go struct field Segment.segments.contents of type models.Content",
"path": [
"GetData"
]
}
],
"data": {
"GetData": null
}
}
```

### Minimal graphql.schema and models to reproduce
```
type Root {
id: String
title: String
segments: [Segment]
}

type Segment {
id: String
contents: [Content]
}

type Team {
name: String
}

type A implements Content {
id: String
title: String
teams: [Team]
}

type B implements Content {
id: String
title: String
score: Int
}

interface Content {
id: String
title: String
}

type Query {
GetData: Root
}
```
Here is complete code:
https://bit.ly/3VGNjus

### versions
- `go run github.com/99designs/gqlgen version`? v0.17.20
- `go version`? go version go1.19 darwin/amd64

这个 issue 涉及 gqlgen 中 GraphQL 接口的 unmarshalling 错误。首先检查提供的 schema 和链接的代码，以了解 Content 接口的实现。查看生成的 models 和 resolvers，尤其是 Segment.contents 字段的处理方式。运行示例以复现错误，然后查阅 gqlgen 关于接口和联合类型的文档，了解应如何配置 unmarshalling。

由索引模型根据 Issue 内容生成。