test: fix pane shell idle foreground-command race (#4691)

The interactive-shell idle test sent SIGINT as soon as it observed the
shell was busy. That condition can be true before the shell finishes
moving the command into its own foreground process group, so the
interrupt could arrive before the command reset its signal dispositions.
The command then survived in a stale foreground group while the shell
showed a prompt, and the pane was never observed idle again.

Run cat and end it with EOF instead. cat blocks on stdin, so the busy
state is stable, and EOF avoids the interrupt/job-control race.

0 files changed, 0 insertions, 0 deletions