Ignore "Content already exists in this project" error

### 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

latest

### What happened?

I haven't tried to reproduce it, but I got this error in a production app:

```
GraphqlResponseError: Request failed due to following response errors:
- Content already exists in this project
```

I assume it occurs when trying to add an issue or pull requse to a project that was already added, but I thought that theGraphQL API is already handling that gracefully. Maybe there is some racing condition?

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

- [ ] yes

首先，使用最新版本以及相关的 Node 或 Deno 环境，重现添加项目中已存在的 issue 或 pull request 时报告的 GraphQLResponseError。将完成定义为能够正常处理且不出现“Content already exists in this project”错误；报告没有提供可供开始的测试用例或文件。

由索引模型根据 Issue 内容生成。