Set TargetFrameworkVersion to v11 for Android

[frederikprijck]

Changes

Updating android to target Android 11 as per https://developer.android.com/google/play/requirements/target-sdk

Note: Even thought this could be seen as a breaking change, it actualy isn't as anything lower isn't suppported anymore by Android so we will include this in a non-major bump.

Checklist

• [x] I have read the Auth0 general contribution guidelines
• [x] I have read the Auth0 Code of Conduct
• [x] All existing and new tests complete without errors
• [x] All code guidelines in the CONTRIBUTING documentation have been run/followed