chore: use JDK 21 release instead of toolchain

Author: cloudshiftchris

.github/workflows/build.yaml

@@ -30,20 +30,14 @@ jobs:
     - name: 'Set up JDK'
       uses: 'actions/setup-java@99b8673ff64fbf99d8d325f52d9a5bdedb8483e9' # v4.2.1
       with:
-        java-version: '17'
-        distribution: 'temurin'
-        check-latest: 'true'
+        java-version: 21
 
     # https://github.com/gradle/actions/tree/main/setup-gradle
     - name: 'Set up Gradle'
       uses: 'gradle/actions/setup-gradle@d9c87d481d55275bb5441eef3fe0e46805f9ef70' # v3.5.0
       with:
         gradle-version: 'wrapper'
-        gradle-home-cache-includes: |-
-          jdks
-          caches
-          notifications
-        gradle-home-cache-cleanup: 'true'
+        gradle-home-cache-cleanup: true
         validate-wrappers: true
 
     # https://github.com/gradle/actions/tree/main/dependency-submission

build.gradle.kts

@@ -4,6 +4,7 @@ import com.ncorti.ktfmt.gradle.tasks.KtfmtFormatTask
 import com.vanniktech.maven.publish.SonatypeHost
 import org.gradle.api.tasks.testing.logging.TestExceptionFormat
 import org.gradle.api.tasks.testing.logging.TestLogEvent
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 /*
  * Copyright 2023 the original author or authors.
@@ -63,7 +64,16 @@ tasks.withType<AbstractArchiveTask>().configureEach {
 
 kotlin {
     explicitApi()
-    jvmToolchain(21)
+}
+
+tasks.withType<KotlinCompile>().configureEach {
+    kotlinOptions {
+        jvmTarget = "21"
+        freeCompilerArgs += listOf(
+            "-Xjsr305=strict",
+            "-Xjdk-release=21"
+        )
+    }
 }
 
 mavenPublishing {