[appletls] Trust SecTrustResult.Proceed as well. Fixes #58411.
Apple states clearly in their documentation about SecTrustResult.Proceed [1]:
The user explicitly chose to trust a certificate in the chain (usually by
clicking a button in a certificate trust panel).
Your app should trust the chain.
This fixes bug #[58411][2], where SecTrustEvaluate returns
SecTrustResult.Proceed starting with iOS 11.
[1]: https://developer.apple.com/documentation/security/
1394363-sectrustevaluate
[2]: https://bugzilla.xamarin.com/show_bug.cgi?id=58411