When one issue has two PRs in the same repository and one PR is in state `open` and another PR is in state `closed`, the method 'IssueWorkItem#run' may get the wrong PR which is in state `closed`.

The related code is shown below. The `findAny` method causes this bug. We should get all the corresponding PRs firstly and then filter the open PRs.

```

        Stream.concat(mainIssue.stream(), backports.stream())
                .flatMap(i -> PullRequestUtils.pullRequestCommentLink(i).stream())
                .map(uri -> bot.repositories().stream()
                        .map(r -> r.parsePullRequestUrl(uri.toString()))
                        .flatMap(Optional::stream)
                        .findAny())
                .flatMap(Optional::stream)
                .map(pr -> new PullRequestWorkItem(pr.repository(), pr.id(), csrIssue.project()))
                .forEach(ret::add);
```