Add JvmTarget6OnJvm8 test suite

compiler/tests-different-jdk/build.gradle.kts

@@ -69,25 +69,23 @@ codegenTest(target = 6, jvm = 6, jdk = "JDK_18") {
     }
 }
 
+//JDK 8
+codegenTest(target = 6, jvm = 8) {}
+
+// This is default one and is executed in default build configuration
 codegenTest(target = 8, jvm = 8) {}
 
-// Switch TC builds to...
+//JDK 11
 codegenTest(target = 6, jvm = 11) {}
 
 codegenTest(target = 8, jvm = 11) {}
 
 codegenTest(target = 11, jvm = 11) {}
 
-//...and delete old tasks..
-codegenTest(target = 6, jvm = 9) {}
-
-codegenTest(target = 8, jvm = 9) {}
-
-codegenTest(target = 9, jvm = 9) {}
-
 //..also add this two tasks to build after adding fresh jdks to build agents
 val mostRecentJdk = JdkMajorVersion.values().last().name
 
+//LAST JDK from JdkMajorVersion available on machine
 codegenTest(target = 6, jvm = "Last", jdk = mostRecentJdk) {
     jvmArgs!!.add( "-XX:-FailOverToOldVerifier")
 }

compiler/tests-different-jdk/tests/org/jetbrains/kotlin/codegen/jdk/CustomJvmTargetOnJvmBaseTest.kt

@@ -36,6 +36,9 @@ abstract class CustomJvmTargetOnJvmBaseTest
 @RunWith(JUnitPlatformRunnerForJdk6::class)
 class JvmTarget6OnJvm6 : CustomJvmTargetOnJvmBaseTest()
 
+@RunWith(JUnitPlatform::class)
+class JvmTarget6OnJvm8 : CustomJvmTargetOnJvmBaseTest()
+
 @RunWith(JUnitPlatform::class)
 class JvmTarget8OnJvm8 : CustomJvmTargetOnJvmBaseTest()