fix(ci): Dynamically set Kotlin language version based on compiler

Kotlin 2.3+ dropped support for language version 1.8. Use 2.0 when
building with Kotlin 2.3+, otherwise keep 1.8.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: romtsn

plugin-build/build.gradle.kts

@@ -5,7 +5,7 @@ import java.util.Properties
 import org.gradle.api.tasks.testing.logging.TestLogEvent
 import org.jetbrains.kotlin.config.KotlinCompilerVersion
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_11
-import org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_1_8
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 plugins {
@@ -91,8 +91,12 @@ tasks.withType<KotlinCompile>().configureEach {
 
   compilerOptions {
     jvmTarget.set(JVM_11)
-    languageVersion.set(KOTLIN_1_8)
-    apiVersion.set(KOTLIN_1_8)
+    // Kotlin 2.3+ dropped support for language version 1.8, so we need to use 2.0 there
+    val kotlinLangVersion =
+      if (KotlinCompilerVersion.VERSION.startsWith("2.3")) KotlinVersion.KOTLIN_2_0
+      else KotlinVersion.KOTLIN_1_8
+    languageVersion.set(kotlinLangVersion)
+    apiVersion.set(kotlinLangVersion)
   }
 }