fix: allow building w/ JDKs beyond Java 17

gradle-plugin/build.gradle.kts

@@ -1,3 +1,5 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 plugins {
     `kotlin-dsl`
     `java-gradle-plugin`
@@ -26,8 +28,19 @@ dependencies {
     compileOnly("org.jetbrains.kotlin:kotlin-gradle-plugin:2.4.0")
 }
 
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
+}
+
 kotlin {
-    jvmToolchain(17)
+    compilerOptions {
+        jvmTarget.set(JvmTarget.JVM_17)
+    }
+}
+
+tasks.withType<JavaCompile>().configureEach {
+    options.release.set(17)
 }
 
 gradlePlugin {