Use the right repository property

The github go library doesn't set the repository property of the issue
on parsing context (as it's js version does). So you have to use the
root Repo property instead

pkg/icassigner/action.go

@@ -140,15 +140,15 @@ func (a *Action) Run(ctx context.Context, event *github.IssuesEvent, dryRun bool
 		return nil
 	}
 
-	if event.Issue.Repository == nil || event.Issue.Repository.Name == nil {
-		log.Fatalf("Can't set any assignee as the repository or its name is missing, payload: %+v", event.Issue.Repository)
+	if event.Repo == nil || event.Repo.Name == nil {
+		log.Fatalf("Can't set any assignee as the repository or its name is missing, payload: %+v", event.Repo)
 	}
 
-	if event.Issue.Repository.Owner == nil || event.Issue.Repository.Owner.Login == nil {
-		log.Fatalf("Can't set any assignee as the repository owner or its login name is missing, payload: %+v", event.Issue.Repository.Owner)
+	if event.Repo.Owner == nil || event.Repo.Owner.Login == nil {
+		log.Fatalf("Can't set any assignee as the repository owner or its login name is missing, payload: %+v", event.Repo.Owner)
 	}
 
-	_, _, err = a.Client.Issues.AddAssignees(ctx, *event.Issue.Repository.Owner.Login, *event.Issue.Repository.Name, *event.Issue.Number, []string{theChosenOne.Name})
+	_, _, err = a.Client.Issues.AddAssignees(ctx, *event.Repo.Owner.Login, *event.Repo.Name, *event.Issue.Number, []string{theChosenOne.Name})
 
 	return err
 }