This was introduced in #7500 to fight `ERROR: The process "4436" not found.`
messages when killing a process that did already exit.
Since then, we no longer inherit stdout/stderr, so the error message
should not appear anymore.
This is a speculative fix to leftover tmp directories.
When users issues SIGINT twice, we enter `gracefullyClose()`
twice, and shortcut the second time. It turns out, we do
not wait for directories removal.
Note: it is unknown how often we reach this codepath in practice.
