Update dependency org.jetbrains.kotlin:kotlin-stdlib to v2.3.21 (#679)

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

Author: renovate[bot]

gradle/libs.versions.toml

@@ -20,7 +20,7 @@ jaxb-api = "4.0.5"
 jaxb-impl = "4.0.7"
 jctools = "4.0.6"
 junit = "4.13.2"
-kotlin = "2.3.20"
+kotlin = "2.3.21"
 logback = "1.5.32"
 mockito = "5.23.0"
 netty = "4.1.132.Final"