fix flake in kube system test

Increase the loop range from 5 to 20 to make sure we give the service
enough time to transition to inactive.  Other tests have the same range
with 0.5 seconds sleeps, so I expect the new value to be sufficient and
consistent.

Fixes: #17093
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

test/system/250-systemd.bats

@@ -431,7 +431,7 @@ EOF
     # design yet for propagating exit codes up to the service
     # container.
     run_podman pod kill test_pod
-    for i in {0..5}; do
+    for i in {0..20}; do
         run systemctl is-active $service_name
         if [[ $output == "inactive" ]]; then
             break