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## Summary
<!-- What's the purpose of the change? What does it do, and why? -->
Fixes#5739
## Test Plan
<!-- How was it tested? -->
Manually tested:
```sh
$ tree dir
dir
├── dir.py
│ └── file.py
└── file.py
1 directory, 2 files
$ cargo run -p ruff_cli -- check dir --no-cache
Finished dev [unoptimized + debuginfo] target(s) in 0.08s
Running `target/debug/ruff check dir --no-cache`
dir/dir.py/file.py:1:7: F821 Undefined name `a`
dir/file.py:1:7: F821 Undefined name `a`
Found 2 errors.
```
Is a unit test needed?
a4e5e3205f