Upgrade Kotlin version to 1.9.21

Author: iamgio

core/src/main/kotlin/eu/iamgio/pikt/util/KotlinCompilerDownloader.kt

@@ -20,7 +20,7 @@ private const val DOWNLOAD_URL = "https://github.com/JetBrains/kotlin/releases/d
 /**
  * Default Kotlin version to download if not specified.
  */
-private const val DEFAULT_KOTLIN_VERSION = "1.7.20"
+private const val DEFAULT_KOTLIN_VERSION = "1.9.21"
 
 /**
  * Downloads the Kotlin compiler from GitHub releases.

pom.xml

@@ -16,7 +16,7 @@
     </modules>
 
     <properties>
-        <kotlin.version>1.7.20</kotlin.version>
+        <kotlin.version>1.9.21</kotlin.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
     </properties>