Update kotlin monorepo to v2.2.21 (#173)

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

Author: renovate[bot]

gradle/libs.versions.toml

@@ -3,7 +3,7 @@ dkimcore = "1.6.1"
 dkim-gradle = "1.4.7"
 dokkatoo = "2.4.0"
 junit = "5.14.0"
-kotlin = "2.2.20"
+kotlin = "2.2.21"
 licenser = "0.6.1"
 mockito-kotlin = "6.1.0"
 nexus-publish-plugin = "2.0.0"