A project can contain issues from other owners, but returned items do not include `.content.owner.login`

### Please avoid duplicates

- [x] I checked [all open bugs](https://github.com/gr2m/github-project/issues?q=is%3Aissue+is%3Aopen+label%3Abug) and none of them matched my problem.

### Reproducible test case

_No response_

### Please select the environment(s) that are relevant to your bug report

- [ ] Browsers
- [ ] Node
- [ ] Deno

### Versions

n/a

### What happened?

Today I learned that an issue that was added to a project might belong to a different owner than the project. Given that is possible, we should load the owner login of items by default.

### Would you be interested in contributing a fix?

- [ ] yes

No file or test is identified in the issue. Trace how project items are loaded and inspect the returned item shape, then ensure an item's owner login is included by default; add or update coverage for an issue belonging to an owner different from the project.

索引モデルが issue の本文から書いたものです。