Don't fail if cron isn't installed when setting up systemd timer (#147)

* `cron` isn't always installed and is not required when using a systemd
  timer, so make sure setup doesn't fail when we check if there's
  already an installed cron timer

Signed-off-by: Woomymy <woomy@woomy.be>

tasks/noauto_create_timer_systemd.yml

@@ -6,11 +6,13 @@
     state: absent
   check_mode: true
   register: cron_file_exists
+  ignore_errors: true
 
 - name: Ensure no Borgmatic Cron file exists.
   ansible.builtin.assert:
     that:
       - not cron_file_exists.changed
+      - not cron_file_exists.failed or "Failed to find" in cron_file_exists.msg
     fail_msg: Found an existing Borgmatic Cron job. Please remove before using Systemd timer.
 
 - name: Create borgbackup timer