Fix empty diff test failure from upstream JavaSourceSet marker updates

openrewrite/rewrite#7202 added JavaSourceSet marker updates to
ChangeDependencyGroupIdAndArtifactId, which now modifies Java files'
markers without changing text content. This causes the test framework
to flag "empty diff" errors for Java source specs without explicit
`after` text.

Provide explicit `after` text (identical to `before`) for the Java
source file in the affected test to accept the marker-only change.

See openrewrite/rewrite#7349 for the upstream issue.

Author: timtebeek

src/test/java/org/openrewrite/java/migrate/javax/AddCommonAnnotationsDependenciesTest.java

@@ -46,6 +46,13 @@ void addDependencyIfAnnotationJsr250Present() {
                 """
                   import javax.annotation.Generated;
 
+                  @Generated("Hello")
+                  class A {
+                  }
+                  """,
+                """
+                  import javax.annotation.Generated;
+
                   @Generated("Hello")
                   class A {
                   }
@@ -94,6 +101,13 @@ void changeAndUpgradeDependencyIfAnnotationJsr250Present() {
                 """
                   import javax.annotation.Generated;
 
+                  @Generated("Hello")
+                  class A {
+                  }
+                  """,
+                """
+                  import javax.annotation.Generated;
+
                   @Generated("Hello")
                   class A {
                   }