De-flakify test

tests/functional/cylc-set/06-parentless/flow.cylc

@@ -1,15 +1,11 @@
 # Start this with --start-task=1800/a.
-# It should stall because x => b is off-flow.
-# The stall handler should unstall it by spawning x.
+# Task a's script should spawn x.
 # The log should show a clock-trigger check before x runs.
 
 [scheduler]
     [[events]]
         inactivity timeout = PT30S
         abort on inactivity timeout = True
-        stall timeout = PT10S
-        abort on stall timeout = True
-        stall handlers = "cylc set --pre=all %(workflow)s//1800/x"
 
 [scheduling]
     initial cycle point = 1800
@@ -19,4 +15,6 @@
             @wall_clock => x => b
         """
 [runtime]
-    [[a, b, x]]
+    [[a]]
+        script = cylc set --pre=all "${CYLC_WORKFLOW_ID}//1800/x"
+    [[b, x]]