Migrate to JDK 17

plugin-build/unmeta/build.gradle.kts

@@ -1,5 +1,3 @@
-import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
-
 plugins {
     signing
     kotlin("jvm")
@@ -18,13 +16,8 @@ dependencies {
 }
 
 java {
-    sourceCompatibility = JavaVersion.VERSION_1_8
-    targetCompatibility = JavaVersion.VERSION_1_8
-}
-
-tasks.withType<KotlinCompile> {
-    kotlinOptions {
-        jvmTarget = JavaVersion.VERSION_1_8.toString()
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(17))
     }
 }