test: Fix race in check-services testing of timers
test: Fix race in check-services testing of timers

The 'Next Run' and 'Last Trigger' columns are updated when the
timer has run. In cases of a heavily loaded system, the timer
completes before the test can continue running, and so the UI
will show a later state than expected.

This race is fundamentally hard to avoid in the testing, so just
losen the testing a bit.

Closes #10048
garrett/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,garrett/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,deryni/cockpit,cockpituous/cockpit,andreasn/cockpit,deryni/cockpit,deryni/cockpit,garrett/cockpit,deryni/cockpit,garrett/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,andreasn/cockpit,mvollmer/cockpit,andreasn/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpituous/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,cockpit-project/cockpit,andreasn/cockpit,garrett/cockpit,martinpitt/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,cockpit-project/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,cockpituous/cockpit,martinpitt/cockpit,martinpitt/cockpit,andreasn/cockpit,andreasn/cockpit,andreasn/cockpit,mvollmer/cockpit,deryni/cockpit,moraleslazaro/cockpit,cockpituous/cockpit