chore(deps): bump rxdart in /packages/user_repository

Bumps [rxdart](https://github.com/ReactiveX/rxdart) from 0.27.7 to 0.28.0.
- [Release notes](https://github.com/ReactiveX/rxdart/releases)
- [Commits](ReactiveX/rxdart@0.27.7...0.28.0)

---
updated-dependencies:
- dependency-name: rxdart
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

packages/user_repository/pubspec.yaml

@@ -16,7 +16,7 @@ dependencies:
     sdk: flutter
   powersync_repository:
     path: ../powersync_repository
-  rxdart: ^0.27.7
+  rxdart: ^0.28.0
   shared:
     path: ../shared