Bugfix: Fix delayed cancelation of some commands

Since restic 0.17.0, some commands no longer promptly reacted to being canceled
via Ctrl-C (SIGINT) and continued to run for a limited amount of time. The most
affected commands were `diff`,`find`, `ls`, `stats` and `rewrite`.

This has been fixed.

https://github.com/restic/restic/issues/4957
https://github.com/restic/restic/pull/4960