Bump syncfusion_flutter_calendar from 20.4.50 to 20.4.51 (#1555)

Bumps [syncfusion_flutter_calendar](https://github.com/syncfusion/flutter-examples) from 20.4.50 to 20.4.51.
- [Release notes](https://github.com/syncfusion/flutter-examples/releases)
- [Commits](https://github.com/syncfusion/flutter-examples/commits)

---
updated-dependencies:
- dependency-name: syncfusion_flutter_calendar
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pubspec.yaml

@@ -53,7 +53,7 @@ dependencies:
   shared_preferences: ^2.0.17
   shimmer: ^2.0.0
   social_share: ^2.2.1
-  syncfusion_flutter_calendar: ^20.2.38
+  syncfusion_flutter_calendar: ^20.4.51
   syncfusion_flutter_datepicker: ^20.2.38
   timelines: ^0.1.0
   tutorial_coach_mark: ^1.2.6