fix: fix compatibility with Vaadin 24.0.0.alpha6

Close #53

Author: javier-godoy

src/main/java/com/flowingcode/vaadin/addons/errorwindow/ErrorWindow.java

@@ -176,7 +176,7 @@ private VerticalLayout createMainLayout() {
 
       // copy details to clipboard button
       Button clipboarButton = new Button(i18n.getClipboard());
-      clipboarButton.addThemeVariants(ButtonVariant.LUMO_TERTIARY);
+      clipboarButton.getThemeNames().add(ButtonVariant.LUMO_TERTIARY.getVariantName());
       clipboarButton.addClickListener(e -> UI.getCurrent().getPage()
           .executeJs("navigator.clipboard.writeText($0)", getStackTrace()));
       clipboarButton.getStyle().set("margin-right", "auto");