change benchmark session to FOLP-ex (faster and less mean squared error than ZF-Constructible);

--- a/src/Pure/Build/build_benchmark.scala	Thu Mar 14 18:08:42 2024 +0100
+++ b/src/Pure/Build/build_benchmark.scala	Fri Mar 15 17:57:03 2024 +0100
@@ -10,9 +10,8 @@
 object Build_Benchmark {
   /* benchmark */
 
-  // ZF-Constructible as representative benchmark session with
-  // short build time and requirements
-  val benchmark_session = "ZF-Constructible"
+  // representative benchmark session with short build time and requirements
+  val benchmark_session = "FOLP-ex"
 
   def benchmark_command(
     host: Build_Cluster.Host,