Updated Kotlin to 2.1.21-RC and KSP to 2.1.21-RC-2.0.0.

Author: ianbrandt

gradle/libs.versions.toml

@@ -10,11 +10,11 @@ junit = "5.12.2"
 jvm-dependency-conflict-resolution = "2.1.2"
 koin = "4.0.4"
 kotest = "5.9.1"
-kotlin = "2.1.20" # Must match KSP version below.
+kotlin = "2.1.21-RC" # Must match KSP version below.
 kotlinpoet = "2.1.0"
 kotlinx-coroutines = "1.10.2"
 kotlinx-dl = "0.5.2"
-ksp = "2.1.20-2.0.0" # Must match Kotlin version above.
+ksp = "2.1.21-RC-2.0.0" # Must match Kotlin version above.
 mockito = "5.17.0"
 mockito-kotlin = "2.2.0"
 mockk = "1.14.0"