[stable-2.11] callback_default test - Reduce sleep time to correct CI failures

For unknown reasons, these tests started failing recently because the results
from testhost11 are being returned before testhost10, but only when coverage is
enabled.

Setting the initial host sleep time to 0 fixes this failure.

ci_coverage
(cherry picked from commit 728e43bc59)

Co-authored-by: Sam Doran <sdoran@redhat.com>

test/integration/targets/callback_default/inventory

@@ -5,6 +5,6 @@ testhost ansible_connection=local ansible_python_interpreter="{{ ansible_playboo
 testhost5 ansible_host=169.254.199.200  # no connection is ever established with this host
 
 [nonlockstep]
-testhost10 i=0.5 ansible_connection=local ansible_python_interpreter="{{ ansible_playbook_python }}"
+testhost10 i=0 ansible_connection=local ansible_python_interpreter="{{ ansible_playbook_python }}"
 testhost11 i=3.0 ansible_connection=local ansible_python_interpreter="{{ ansible_playbook_python }}"
 testhost12 i=12.0 ansible_connection=local ansible_python_interpreter="{{ ansible_playbook_python }}"