Update KSP version to 2.0.21

This commit updates the KSP dependency from version 2.0.20-1.0.25 to 2.0.21-1.0.25 in the gradle/libs.versions.toml file.

gradle/libs.versions.toml

@@ -12,7 +12,7 @@ dokka = "1.9.20"
 # https://github.com/willowtreeapps/assertk
 assertk = "0.28.1"
 # https://github.com/google/ksp/releases
-ksp = "2.0.20-1.0.25"
+ksp = "2.0.21-1.0.25"
 
 [libraries]
 gradle-kotlin-plugin = { module = "org.jetbrains.kotlin:kotlin-gradle-plugin", version.ref = "kotlin" }