Gradle: Upgrade mockk to version 1.12.5

See: https://github.com/mockk/mockk/releases/tag/1.12.5
Signed-off-by: Marcel Bochtler <git@bochtler.io>

gradle/libs.versions.toml

@@ -51,7 +51,7 @@ log4jApiKotlin = "1.2.0"
 maven = "3.8.6"
 # @pin this version as it needs to be aligned with "maven".
 mavenResolver = "1.7.3"
-mockk = "1.12.4"
+mockk = "1.12.5"
 okhttp = "4.9.3"
 poiOoxml = "5.2.2"
 postgres = "42.4.1"