unnecessary entity resolvers generated when having multiple keys even after setting resolvable: false

### What happened?
When there is only one key defined for a type and setting resolvable as false, gqlgen is able to avoid generating unnecessary entity resolver for that key.
However, when there are multiple keys defined for a type, even though I set resolvable as false, the entity resolvers are still generated for each key.

### What did you expect?
After setting resolvable: false, no entity resolver to be generated for the type.

### Minimal graphql.schema and models to reproduce
User subgraph/service:
```
type User @key(fields: "id", resolvable: false) @key(fields: "name", resolvable: false) {
id: ID!
name: String!
}
```

### versions
- `go run github.com/99designs/gqlgen version`?
gqlgen@v0.17.45
- `go version`?
go version go1.22.1 X:nocoverageredesign darwin/arm64