Adjust the ingestion script / aclpub checker

### Confirm that this is a bug report

- [X] I want to report an issue that does _not_ concern paper or author metadata.
- [X] I have searched for similar existing issues first.

### Problem Description

Check for
- "the the" (after lowercasing)
- "The" in the middle of a booktitle.

The issue names the ingestion script and aclpub checker but no file or test. Start by locating that checker and inspecting how booktitle text is validated; verify behavior for lowercased "the the" and "The" in the middle of a booktitle. Done means both cases are checked as intended.

由索引模型根据 Issue 内容生成。