fix: note editor italic (#5230)

web/app/components/workflow/note-node/note-editor/theme/index.ts

   },
   link: 'note-editor-theme_link',
   text: {
+    italic: 'note-editor-theme_text-italic',
     strikethrough: 'note-editor-theme_text-strikethrough',
   },
 }

web/app/components/workflow/note-node/note-editor/theme/theme.css

 
 .note-editor-theme_text-strikethrough {
   text-decoration: line-through;
+}
+
+.note-editor-theme_text-italic {
+  font-style: italic;
 }