Bump kotlin-stdlib-jdk8 from 1.6.20 to 1.6.21

Bumps [kotlin-stdlib-jdk8](https://github.com/JetBrains/kotlin) from 1.6.20 to 1.6.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.6.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.6.20...v1.6.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib-jdk8
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

build.gradle

@@ -14,7 +14,7 @@ repositories {
 }
 
 dependencies {
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.6.20"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.6.21"
     implementation "org.jetbrains.kotlinx:kotlinx-serialization-core-jvm:1.3.2"
     implementation "com.amazon.ion:ion-java:1.9.4"
     testImplementation "io.kotest:kotest-runner-junit5:5.2.2"