fix #4483: fix `task log` command interrupt handling

fix #4483: fix `task log` command interrupt handling

`proxmox-backup-client task log ..` and `proxmox-backup-manager task log ..`
are used to view the logs of tasks that have been started by another client, so
interrupting the task progress view should not forward the interrupt to the
running task. other call sites of the same helper(s) that spawn a task and then
print its progress should keep the old behaviour of interrupting the spawned
task on C^c.

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>