嵌套接口：X未实现Y（Z方法的类型错误）

In one package I have an interface Repository that has a method GetReporter that returns an interface Reporter. This is used by a function Execute that takes a Repository and gets its Reporter via the GetReporter function.

In another package I have a struct GithubRepository that has a method GetReporter that returns a GithubReporter.

In a third package I want to call the Execute function out of package #1 with a GithubRepository instance.

I am trying to have package 1 and 2 independent of each other, without one importing something from the other. The 3rd package should combine the first two.

Golang returns:

cannot use githubRepository (type GithubRepository) as type Repository in argument to Execute:
    GithubRepository does not implement Repository (wrong type for GetReporter method)
        have GetReporter(string) GithubReporter
        want GetReporter(string) Reporter

Code:

package main

// Package #1

type Repository interface {
  GetReporter(string) Reporter
}

type Reporter interface {
  ChangeStatus(string) error
}

func Execute(r Repository) {
  // Do something with the repository
}

// Package #2

type GithubRepository struct {
}

type GithubReporter struct {
}

func (repo *GithubRepository) GetReporter(sha string) GithubReporter {
 return GithubReporter{}
}

func (reporter *GithubReporter) ChangeStatus(status string) error {
  // Change the status
  return nil
}

// Package #3

func main() {
  githubRepository := GithubRepository{}
  Execute(githubRepository)
}

Go Playground: https://play.golang.org/p/ph0sZnyAC5I