Pass `hold: true` to Alacritty for tasks (#13898)

It seems `hold: false` causes alacritty to close the channel earlier,
without waiting for the output from the child command to go to Zed.

Fixes [#13683](https://github.com/zed-industries/zed/issues/13683)

Release Notes:

- Fixed loosing output of a spawned task
([#13683](https://github.com/zed-industries/zed/issues/13683)).

[Screencast from 2024-07-06
18-28-56.webm](https://github.com/zed-industries/zed/assets/39293/4ebef8b5-7c0d-46be-9341-4ac0d809458d)