Update kotlin monorepo to v2.0.21 (#10)

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

Author: renovate[bot]

gradle/libs.versions.toml

@@ -16,7 +16,7 @@ detektEygraber = "1.0.11"
 
 dokka = "1.9.20"
 
-kotlin = "2.0.20"
+kotlin = "2.0.21"
 
 ktlint = "1.3.1"