Update kotlin (#15)

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

Author: renovate[bot]

gradle/libs.versions.toml

@@ -1,14 +1,14 @@
 [versions]
 
-kotlin = "2.0.20"
+kotlin = "2.0.21"
 jdkTarget = "8"
 jvmToolchain = "21"
 kotlinTarget = "1.9.0"
 ktor2 = "2.3.13"
 ktor3 = "3.0.1"
-kotlinx-serialization = "1.7.1"
+kotlinx-serialization = "1.7.3"
 kotlinx-datetime = "0.6.1"
-poko = "0.17.0"
+poko = "0.17.2"
 kermit = "2.0.4"
 spotless = "7.0.0.BETA2"
 vanniktech-maven = "0.29.0"