Rename test class to NestedTests for AOT integration testing

Prior to this commit, the NestedTestCase resulted in errors during our
AOT end-to-end integration tests since it did not comply to our "*Tests"
naming convention.

See spring-projectsgh-29122

spring-test/src/test/java/org/springframework/test/context/junit4/nested/NestedTestsWithSpringRulesTests.java

@@ -54,7 +54,7 @@ public void topLevelTest() {
 
 
 	@ContextConfiguration(classes = NestedConfig.class)
-	public class NestedTestCase extends SpringRuleConfigurer {
+	public class NestedTests extends SpringRuleConfigurer {
 
 		@Autowired
 		String bar;