Bump org.jetbrains.kotlin:kotlin-bom from 1.9.20 to 1.9.21

Bumps [org.jetbrains.kotlin:kotlin-bom](https://github.com/JetBrains/kotlin) from 1.9.20 to 1.9.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/compare/v1.9.20...v1.9.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-bom
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

gradle/libs.versions.toml

@@ -9,7 +9,7 @@ org-apache-maven-resolver = "1.9.17"
 org-aspectj = "1.9.20.1"
 org-bouncycastle = "1.70"
 org-eclipse-jetty = "11.0.18"
-org-jetbrains-kotlin = "1.9.20"
+org-jetbrains-kotlin = "1.9.21"
 org-jetbrains-kotlinx = "1.7.3"
 org-mockito = "5.5.0"
 org-opensaml = "4.3.0"