Add support for 1.9.21.

Author: FilipDolnik

common-gradle/gradle.properties

@@ -8,7 +8,7 @@ kotlin.mpp.import.enableKgpDependencyResolution=true
 
 pluginId=co.touchlab.skie
 
-versionSupport.kotlinTooling=1.8.0(1.8.10), 1.8.20(1.8.21, 1.8.22), 1.9.0(1.9.10), 1.9.20
+versionSupport.kotlinTooling=1.8.0(1.8.10), 1.8.20(1.8.21, 1.8.22), 1.9.0(1.9.10), 1.9.20(1.9.21)
 versionSupport.gradleApi=7.3, 8.0, 8.1
 
 touchlab.key=ABCDEFGHIJKLMNOPQRSTUVWXYZ