chore(deps): update kotlin to v2.0.21 (open-telemetry#629)

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

Author: renovate[bot]

demo-app/gradle/libs.versions.toml

@@ -3,7 +3,7 @@ opentelemetry = "1.42.1"
 opentelemetry-alpha = "1.42.1-alpha"
 junit = "5.11.2"
 spotless = "6.25.0"
-kotlin = "2.0.20"
+kotlin = "2.0.21"
 navigation-compose = "2.7.7"
 
 [libraries]

gradle/libs.versions.toml

@@ -10,7 +10,7 @@ junit = "5.11.2"
 byteBuddy = "1.15.4"
 okhttp = "4.12.0"
 spotless = "6.25.0"
-kotlin = "2.0.20"
+kotlin = "2.0.21"
 androidPlugin = "8.7.0"
 junitKtx = "1.2.1"
 autoService = "1.1.1"