more robust test: avoid spurious Interrupt (stack overflow?) due to List.fun_lub_parametric;

--- a/src/Benchmarks/Quickcheck_Benchmark/Find_Unused_Assms_Examples.thy	Thu Apr 11 12:38:22 2019 +0200
+++ b/src/Benchmarks/Quickcheck_Benchmark/Find_Unused_Assms_Examples.thy	Thu Apr 11 12:41:50 2019 +0200
@@ -27,7 +27,10 @@
 
 context notes [[quickcheck_finite_types = true]]
 begin
-  find_unused_assms List
+  context notes [[quickcheck_finite_type_size = 2]]
+  begin
+    find_unused_assms List
+  end
   find_unused_assms Map
 end