Follow-up of https://github.com/zed-industries/zed/pull/28993

* Tone down tasks' cancellation logging
* Fix task terminals' leak, disallowing to fully cancel the task by
dropping the terminal off the pane:

https://github.com/zed-industries/zed/blob/f619d5f02af100c34e286af294a42a01dcfb238c/crates/terminal_view/src/terminal_panel.rs#L1464-L1471

Release Notes:

- Fixed tasks not being stopped on reruns