chore(deps): update kotest to v6.1.5 (#973)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

gradle/libs.versions.toml

@@ -1,6 +1,6 @@
 [versions]
 alchemist = "43.0.12"
-kotest = "6.1.4"
+kotest = "6.1.5"
 
 [libraries]
 alchemist = { module = "it.unibo.alchemist:alchemist", version.ref = "alchemist" }