Accept marker-only changes in RewriteTest instead of failing with empty diff

After #7202, `ChangeDependencyGroupIdAndArtifactId` updates `JavaSourceSet`
markers on Java files when dependency coordinates change. These marker-only
changes produce Results with identical before/after text, which
`RewriteTest` previously treated as errors ("An empty diff was generated").

Instead of failing, silently accept Results where the printed text is
unchanged. This allows recipes to update markers (e.g. classpath metadata)
without requiring downstream tests to add explicit `after` text for every
Java source spec.

The `afterRecipe` callback still fires with the updated tree, so tests
that need to verify marker changes (like `updatesJavaSourceSetMarkerOnJavaFiles`)
continue to work.

Fixes #7349

Author: timtebeek

rewrite-test/src/main/java/org/openrewrite/test/RewriteTest.java

@@ -562,7 +562,16 @@ default void rewriteRun(Consumer<RecipeSpec> spec, SourceSpec<?>... sourceSpecs)
                             boolean isRemote = result.getAfter() instanceof Remote;
                             if (!isRemote && Objects.equals(result.getBefore().getSourcePath(), result.getAfter().getSourcePath()) &&
                                 Objects.equals(before, actualAfter)) {
-                                fail("An empty diff was generated. The recipe incorrectly changed a reference without changing its contents.");
+                                // Marker-only changes (e.g. JavaSourceSet updates from dependency
+                                // coordinate changes) produce Results with identical text. Accept
+                                // these silently rather than treating them as errors.
+                                allResults.remove(result);
+                                try {
+                                    //noinspection unchecked
+                                    ((Consumer<SourceFile>) sourceSpec.afterRecipe).accept(result.getAfter());
+                                } catch (ClassCastException ignored) {
+                                }
+                                continue nextSourceFile;
                             }
 
                             assert result.getBefore() != null;