Make inner test class static

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=173413495

javatests/google/registry/util/SerializeUtilsTest.java

@@ -29,7 +29,7 @@ import org.junit.runners.JUnit4;
 @RunWith(JUnit4.class)
 public class SerializeUtilsTest {
 
-  class Lol {
+  static class Lol {
     @Override
     public String toString() {
       return "LOL_VALUE";