Flaky test: TestSlowStdinClosing

Seen failing on Windows 2022 / c8d on https://github.com/moby/moby/pull/42993 / https://ci-next.docker.com/public/blue/organizations/jenkins/moby/detail/PR-42993/3/pipeline


```
=== RUN   TestDockerSuite/TestSlowStdinClosing
    docker_cli_run_test.go:4177: assertion failed: error is not nil: exit status 127
    --- FAIL: TestDockerSuite/TestSlowStdinClosing (0.92s)
```