Fixed regression: trivial error on String comparison

Fix #5423

The regression has been introduced in:
72f815b Refactor file adding and renaming, and save as handling

Author: cmaglie

arduino-core/src/processing/app/Sketch.java

@@ -250,7 +250,7 @@ protected File checkNewFoldername(File newFolder) throws IOException {
     // If the folder is actually renamed (as opposed to moved somewhere
     // else), check for conflicts using the new filename, but the
     // existing folder name.
-    if(newFolder.getName() != folder.getName())
+    if (!newFolder.getName().equals(folder.getName()))
       checkNewFilename(new File(folder, newPrimary));
 
     return new File(newFolder, newPrimary);