Update kotest to v6

Author: renovate[bot]

gradle/libs.versions.toml

@@ -12,7 +12,7 @@ kfsm = "0.12.0"
 # kfsm-v2 2.2+ changed Outbox method signatures to return Result<…>.
 # Pinned to 2.1.0 until InMemoryOutbox and related code are updated to match.
 kfsmv2 = "2.1.0"
-kotest = "5.9.1"
+kotest = "6.1.11"
 kotlinxCoroutines = "1.10.2"
 kotestArrow = "2.0.0"
 # @pin