`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

使用列出的 mypy 命令和 opentelemetry 导入，通过 file.py 重现交替结果，然后追踪与 unused-ignore 状态相关的缓存处理。为重复的缓存运行添加回归测试；当该命令始终不报告无端的 [unused-ignore] 错误时，即表示完成。