refactor: RewriteTest classes should not be public

Use this link to re-run the recipe: https://app.moderne.io/recipes/org.openrewrite.java.recipes.RewriteTestClassesShouldNotBePublic?organizationId=T3BlblJld3JpdGU%3D

Co-authored-by: Moderne <[email protected]>

src/test/java/org/openrewrite/java/testing/junit5/AssertTrueInstanceofToAssertInstanceOfTest.java

@@ -24,7 +24,7 @@
 
 import static org.openrewrite.java.Assertions.java;
 
-public class AssertTrueInstanceofToAssertInstanceOfTest implements RewriteTest {
+class AssertTrueInstanceofToAssertInstanceOfTest implements RewriteTest {
     @Override
     public void defaults(RecipeSpec spec) {
         spec

src/test/java/org/openrewrite/java/testing/junit5/RemoveDuplicateTestTemplatesTest.java

@@ -25,7 +25,7 @@
 
 import static org.openrewrite.java.Assertions.java;
 
-public class RemoveDuplicateTestTemplatesTest implements RewriteTest {
+class RemoveDuplicateTestTemplatesTest implements RewriteTest {
     @Override
     public void defaults(RecipeSpec spec) {
         spec

src/test/java/org/openrewrite/java/testing/junit5/UpgradeOkHttpMockWebServerTest.java

@@ -26,7 +26,7 @@
 import static org.openrewrite.java.Assertions.mavenProject;
 import static org.openrewrite.maven.Assertions.pomXml;
 
-public class UpgradeOkHttpMockWebServerTest implements RewriteTest {
+class UpgradeOkHttpMockWebServerTest implements RewriteTest {
 
     @Override
     public void defaults(RecipeSpec spec) {

src/test/java/org/openrewrite/java/testing/junit5/UseXMLUnitLegacyTest.java

@@ -23,7 +23,7 @@
 import static org.openrewrite.java.Assertions.mavenProject;
 import static org.openrewrite.maven.Assertions.pomXml;
 
-public class UseXMLUnitLegacyTest implements RewriteTest {
+class UseXMLUnitLegacyTest implements RewriteTest {
     @Override
     public void defaults(RecipeSpec spec) {
         spec