refactor: Java 21 for tests

Use this link to re-run the recipe: https://app.moderne.io/builder/VAYPd4TEG?organizationId=ODQ2MGExMTUtNDg0My00N2EwLTgzMGMtNGE1NGExMTBmZDkw

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

Author: 2 people

src/test/java/org/openrewrite/java/migrate/Java8toJava11Test.java

@@ -63,7 +63,7 @@ void needToJaxb2MavenPlugin() {
                   """,
                 after -> after.after(pomXml -> pomXml)
                   .afterRecipe(doc -> assertThat(doc.getMarkers().findFirst(MavenResolutionResult.class))
-                    .hasValueSatisfying(mrr -> mrr.getPom().getPlugins().get(0).getVersion().startsWith("2.5.")))
+                    .hasValueSatisfying(mrr -> mrr.getPom().getPlugins().getFirst().getVersion().startsWith("2.5.")))
               )
             ),
             8)