Reverting pitest version bump (#843)

Bumping versions breaking functional tests, will need to be investigated further

Author: larslnde

build.gradle

@@ -305,8 +305,8 @@ def versions = [
   springDoc    : '2.6.0',
   springBoot   : '3.3.0',
   serenity     : '3.9.8',
-  gradlePitest  : '1.15.0',
-  pitest       : '1.18.1',
+  gradlePitest  : '1.9.11',
+  pitest       : '1.15.0',
   sonarPitest   : '0.5',
   logbook      : '3.10.0',
   tomcat       : '10.1.33',