Update Kotlin core dependencies

Author: renovate[bot]

gradle/libs.versions.toml

@@ -1,11 +1,11 @@
 [versions]
-kotlin = "1.9.10"
+kotlin = "1.9.21"
 jetbrains-annotations = "24.0.1"
 save-cli = "0.4.0-SNAPSHOT"
 ktor = "2.3.6"
 okio = "3.3.0"
-serialization = "1.6.0"
-kotlinx-datetime = "0.4.1"
+serialization = "1.6.2"
+kotlinx-datetime = "0.5.0"
 kotlinx-coroutines = "1.7.3"
 kotlin-wrappers = "1.0.0-pre.634"
 spring-boot = "2.7.17"