[Test] Properly dispose class loader for running BB tests

compiler/tests-common-new/tests/org/jetbrains/kotlin/test/backend/handlers/JvmBoxRunner.kt

@@ -43,6 +43,7 @@ class JvmBoxRunner(testServices: TestServices) : JvmBinaryArtifactHandler(testSe
         val ktFiles = info.classFileFactory.inputFiles
         val reportProblems = module.targetBackend !in module.directives[CodegenTestDirectives.IGNORE_BACKEND]
         val classLoader = createAndVerifyClassLoader(module, info.classFileFactory, reportProblems)
+        try {
             for (ktFile in ktFiles) {
                 val className = ktFile.getFacadeFqName() ?: continue
                 val clazz = classLoader.getGeneratedClass(className)
@@ -58,6 +59,9 @@ class JvmBoxRunner(testServices: TestServices) : JvmBinaryArtifactHandler(testSe
                 )
                 return
             }
+        } finally {
+            classLoader.dispose()
+        }
     }
 
     private fun callBoxMethodAndCheckResultWithCleanup(