Update dependency org.jetbrains.kotlin.plugin.serialization to v2.3.21 (#175)

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

Author: renovate[bot]

gradle/libs.versions.toml

@@ -14,7 +14,7 @@ kotlinx_serialization = "1.11.0"
 ktor = "3.4.3"
 logback = "1.5.32"
 prometheus = "1.16.5"
-serialization = "2.3.20"
+serialization = "2.3.21"
 release = "3.1.0"
 
 [libraries]