Emitted when all or part of the label's text is copied to the clipboard. Text is normally copied to the clipboard when the user selects a region of text and then copies it using CTRL+C or right clicking to bring up a context menu.
When this signal is emitted, the label whose text was copied is passed to the callback.
This signal cannot be emitted unless the label has been made selectable by passing true to set_selectable() , because text that is not selectable cannot be copied to the clipboard.
Callback function