Update Kotlin and KSP to v2.1.21

Author: renovate[bot]

gradle/libs.versions.toml

@@ -15,7 +15,7 @@ dagger = "2.56.2"
 hamcrest = "2.2"
 jsonUnit = "4.1.1"
 jvm = "17"
-kotlin = "2.1.20"
+kotlin = "2.1.21"
 kotlinCoroutines = "1.10.1"
 ktlint = "1.5.0"
 ktlintGradle = "12.2.0"