testsuite: Increase tolerance of T16916

T16916 (testing #16916) has been slightly fragile in CI due to its
reliance on CPU times. While it's hard to see how to eliminate
the time-dependence entirely, we can nevertheless make it more tolerant.

Fixes #16966.

testsuite/tests/lib/base/T16916.hs

@@ -46,4 +46,4 @@ main = do
 
   -- CPU consumption should roughly be the same when just idling vs
   -- when idling after the event been triggered
-  print $ eventTriggeredUsage / noEventUsage < 10.0
+  print $ eventTriggeredUsage / noEventUsage < 100.0