Make text field of TextFinder example read-only

The text field in Text Finder example ( https://doc.qt.io/qt-6/qtuitools-textfinder-example.html ) is editable. However editing it will break the actual text finding functionality as highlights are no longer cleared:

While it is not crucial for the example that the finding functionality is perfect, it would be a very low-hanging fruit to just disable editing from the text field.