chore(core-deps): update kotlin monorepo to v2.1.21 (#1)

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

Author: renovate[bot]

gradle/libs.versions.toml

@@ -11,7 +11,7 @@ junit = "5.11.4"
 konf = "1.1.2"
 kotest = "6.0.0.M1"
 ktor = "2.3.13"
-kotlin = "2.1.0"
+kotlin = "2.1.21"
 mockito = "5.15.2"
 protelis = "17.7.1"
 react = "19.0.0-pre.854"