fix: set Kotlin API Version to 1.6

Ensures that the compiled code is compatible with older versions of
Kotlin.
In the modelix.samples project this fixes an incompatibility with
the Kotlin version used by Quarkus (1.7).

Author: slisson

build.gradle.kts

@@ -77,9 +77,12 @@ subprojects {
     }
 
     tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>().all {
-        kotlinOptions {
-            jvmTarget = "11"
-            freeCompilerArgs += listOf("-Xjvm-default=all-compatibility")
+        if (!name.lowercase().contains("test")) {
+            kotlinOptions {
+                jvmTarget = "11"
+                freeCompilerArgs += listOf("-Xjvm-default=all-compatibility")
+                apiVersion = org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_1_6.version
+            }
         }
     }
 }