zpool: reduce disk usage in integration tests by using sparse files (#12128)

* zpool: use sparse files in integration tests to reduce diskspace usage

* changelog: add PR link to zpool disk space fragment

* remove changelog fragment for test-only change

tests/integration/targets/zpool/aliases

@@ -11,4 +11,3 @@ skip/macos
 skip/rhel
 skip/docker
 skip/alpine  # TODO: figure out what goes wrong
-skip/ubuntu26.04  # TODO: VM seems to have less disk space than required

tests/integration/targets/zpool/tasks/main.yml

@@ -8,7 +8,7 @@
   block:
     - name: Ensure disk files exists
       ansible.builtin.command:
-        cmd: "dd if=/dev/zero of={{ item }} bs=1M count=256 conv=fsync"
+        cmd: "truncate -s 256M {{ item }}"
         creates: "{{ item }}"
       loop: "{{ zpool_disk_configs }}"