chore: add const to remove flutter warnings

frontend/app_flowy/lib/workspace/presentation/plugins/doc/document.dart

@@ -179,7 +179,7 @@ class DocumentShareButton extends StatelessWidget {
         switch (action) {
           case ShareAction.markdown:
             context.read<DocShareBloc>().add(const DocShareEvent.shareMarkdown());
-            BubbleNotification(
+            const BubbleNotification(
                     msgTitle: 'Exported Complete ^_^',
                     msgBody: "Check in the flowy folder inside your documents directory")
                 .show(context);

frontend/app_flowy/lib/workspace/presentation/widgets/dialogs.dart

@@ -248,7 +248,7 @@ class _BubbleNotification extends State<BubbleNotification> {
               child: ListTile(
                 leading: SizedBox.fromSize(
                   size: const Size(40, 40),
-                  child: ClipOval(
+                  child: const ClipOval(
                     child: Icon(Icons.file_copy),
                   ),
                 ),