Add a separate test configurations for JDK 21 dependent test

After it's released, there would be no need in them, but right now
they are unavailable through the toolchain, so we can't require it.
See KT-58765 for tracking

But there should be a dedicated Build configuration with JDK_21_0 env
properly set.

^KT-58716 Fixed

compiler/tests-common/tests/org/jetbrains/kotlin/test/KotlinTestUtils.java

@@ -197,6 +197,9 @@ public class KotlinTestUtils {
         else if (jdkKind == TestJdkKind.FULL_JDK_17) {
             configuration.put(JVMConfigurationKeys.JDK_HOME, KtTestUtil.getJdk17Home());
         }
+        else if (jdkKind == TestJdkKind.FULL_JDK_21) {
+            configuration.put(JVMConfigurationKeys.JDK_HOME, KtTestUtil.getJdk21Home());
+        }
         else if (JavaVersion.current().compareTo(JavaVersion.compose(9)) >= 0) {
             configuration.put(JVMConfigurationKeys.JDK_HOME, new File(System.getProperty("java.home")));
         }