fix(deps): Update kotlin monorepo to v2.1.21 (#419)

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

Author: renovate[bot]

gradle/kotlinx.versions.toml

@@ -1,5 +1,5 @@
 [versions]
-kotlin = "2.1.0"
+kotlin = "2.1.21"
 serialization = "1.7.3"
 xml_serialization = "0.90.3"