Make tests that wait for concurrent work wait on the event or a condition with a long deadline (issue 1814)

A test that slept a fixed time and then asserted what a goroutine, process or
watcher did failed under the checker's load. Each now waits for its positive
evidence (a started baseline, a call counted, a state reached) within 30 s, and
the concurrency-limit tests meet at a barrier instead of overlapping by sleep.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

modules/dunst/cmd/dunst-tools/actions_test.go

@@ -47,7 +47,7 @@ func TestANotificationsChosenAnswerIsSaidAsAnEvent(t *testing.T) {
 	if !strings.Contains(string(asked), "[--expire-time=0][--wait][--action=a1b2=Release][--action=c3d4=Stop][--]") {
 		t.Fatalf("notify-send was asked %s", asked)
 	}
-	deadline := time.Now().Add(3 * time.Second)
+	deadline := time.Now().Add(30 * time.Second)
 	for {
 		mu.Lock()
 		n := len(said)