`type: ignore` comments on imports of external package lead to `[unused-ignore]` error codes every other run

Bug Report

When running mypy with --warn-unused-ignore --no-namespace-packages --warn-unused-ignores --ignore-missing-imports, putting a type: ignore[attr-defined] on an import will have mypy report an Unused "type: ignore" comment [unused-ignore] every other run, unless the cache is being cleared between runs.

To Reproduce

from opentelemetry.instrumentation.asgi import (  # type: ignore[attr-defined]
    OpenTelemetryMiddleware,
)

(Since this only seems to work with external packages, some setup is required)

1. Run pip install opentelemetry-instrumentation-asgi opentelemetry-distro
2. Add the code snippet below to file.py
3. Run mypy --warn-unused-ignore --no-namespace-packages --warn-unused-ignores --ignore-missing-imports file.py: Observer no error
4. Run mypy --warn-unused-ignore --no-namespace-packages --warn-unused-ignores --ignore-missing-imports file.py: Observe an [unused-ignore] error
5. Run mypy --warn-unused-ignore --no-namespace-packages --warn-unused-ignores --ignore-missing-imports file.py: Observer no error
6. Repeat the cycle as many times as you like :)

When removing the cache between runs, all works well, so I suspect it has something to do with caching.

Your Environment

• Mypy version used: 1.18.2, main
• Mypy command-line flags: --warn-unused-ignore --no-namespace-packages --warn-unused-ignores --ignore-missing-imports
• Mypy configuration options from mypy.ini (and other config files): -
• Python version used: 3.13.7

指定された mypy コマンドと opentelemetry のインポートを使用して file.py で交互に変化する結果を再現し、その後 unused-ignore の状態に関するキャッシュ関連の処理を追跡します。キャッシュされた状態での実行を繰り返す回帰テストを追加します。完了の条件は、コマンドが一貫して不要な [unused-ignore] エラーを報告しないことです。