fix: Implement no-op for cleanUpDanglingCalls method in FlutterWebAuthWeb.

[ab-kapoor]

Issue: PlatformException(Unimplemented, null, The flutter_web_auth plugin for web doesn't implement the method 'cleanUpDanglingCalls', null) is thrown for flutter web app.

This pull request includes a small change to the lib/flutter_web_auth_web.dart file. The change adds a new case to the switch statement in the FlutterWebAuthWeb class to handle cleanUpDanglingCalls without performing any operations.

[maxbeech]

Can we merge this please?