Bump file_picker to 3.0.2+2

With version 3.0.2 `name` of the file_picker library becomes
non-nullable, so a warning was issued for users who had already
used version 3.0.2, as we still assumed that `name` is nullable.
Increasing the version and removing the exclamation mark removes
the warning.

lib/src/widgets/toolbar/image_button.dart

@@ -80,7 +80,7 @@ class ImageButton extends StatelessWidget {
     }
 
     // Take first, because we don't allow picking multiple files.
-    final fileName = result.files.first.name!;
+    final fileName = result.files.first.name;
     final file = File(fileName);
 
     return onImagePickCallback!(file);

pubspec.yaml

@@ -13,7 +13,7 @@ dependencies:
   flutter:
     sdk: flutter
   collection: ^1.15.0
-  file_picker: ^3.0.0
+  file_picker: ^3.0.2+2
   filesystem_picker: ^2.0.0-nullsafety.0
   flutter_colorpicker: ^0.4.0
   flutter_keyboard_visibility: ^5.0.0