Look into Attempt to present UIAlertController which is already presenting warning

[njarecha]

While presenting an alert to enter the password for client certificate, seeing warning related to `already presenting

2023-01-23 14:45:44.896226-0800 AuthenticationExample[28329:387920] [DocumentManager] The view service did terminate with error: Error Domain=_UIViewServiceErrorDomain Code=1 "(null)" UserInfo={Terminated=disconnect method}
2023-01-23 14:45:45.005242-0800 AuthenticationExample[28329:387920] [LayoutConstraints] Changing the translatesAutoresizingMaskIntoConstraints property of a UICollectionViewCell that is managed by a UICollectionView is not supported, and will result in incorrect self-sizing. View: <_UIAlertControllerTextFieldViewCollectionCell: 0x13f4083f0; frame = (0 0; 270 24); gestureRecognizers = <NSArray: 0x600001df2520>; layer = <CALayer: 0x6000013beca0>>
2023-01-23 14:45:45.434019-0800 AuthenticationExample[28329:387920] [Presentation] Attempt to present <UIAlertController: 0x149177400> on <_TtGC7SwiftUI19UIHostingControllerGVS_15ModifiedContentVS_7AnyViewVS_12RootModifier__: 0x149027800> (from <UIViewController: 0x13f228090>) which is already presenting <UIAlertController: 0x13d812800>.

Also, test showCertificateImportError which uses Task.sleep to avoid the already presenting warning. If see the warning then try using MainActor.

[njarecha]

See #243 (comment) for details.