Bugfix: Allow use of rclone/sftp backend when running restic in background

When starting restic in the background, this could result in unexpected behavior
when using the rclone or sftp backend.

For example running `restic -r rclone:./example --insecure-no-password init &`
could cause the calling `bash` shell to exit unexpectedly.

This has been fixed.

https://github.com/restic/restic/issues/5354
https://github.com/restic/restic/pull/5358
https://github.com/restic/restic/pull/5493
https://github.com/restic/restic/pull/5494