Fix Xcode 26 protocol-witness availability error

Xcode 26 tightened protocol-witness availability rules. When one class
satisfies two presentation-context protocols of differing availability —
ASWebAuthenticationPresentationContextProviding (iOS 12+) and
ASAuthorizationControllerPresentationContextProviding (iOS 13+) — the
shared 'presentationAnchor(for:)' witnesses can no longer be guarded
with @available individually on the same type.

Move each protocol conformance into its own extension with the
appropriate @available attribute. The class itself stays unannotated
(callers in ASWebServiceAuthentication and AppleSignInWebService are
already iOS 12+/13+), and the framework's iOS 10 deployment target is
preserved.

Author: ssathy2

IFTTT SDK/AuthenticationSessionPresentationContextProvider.swift

@@ -7,11 +7,10 @@
 
 import AuthenticationServices
 
-/// A class that conforms to `ASWebAuthenticationPresentationContextProviding`.
-class AuthenticationSessionContextPresentationProvider: NSObject, ASWebAuthenticationPresentationContextProviding, ASAuthorizationControllerPresentationContextProviding {
+class AuthenticationSessionContextPresentationProvider: NSObject {
     /// The window context that the presentation of the authentication should take place in.
     private let presentationContext: UIWindow
-    
+
     /// Creates an instance of `AuthenticationSessionContextProvider`.
     ///
     /// - Parameters:
@@ -20,13 +19,17 @@ class AuthenticationSessionContextPresentationProvider: NSObject, ASWebAuthentic
         self.presentationContext = presentationContext
         super.init()
     }
-    
-    @available(iOS 12.0, *)
+}
+
+@available(iOS 12.0, *)
+extension AuthenticationSessionContextPresentationProvider: ASWebAuthenticationPresentationContextProviding {
     func presentationAnchor(for session: ASWebAuthenticationSession) -> ASPresentationAnchor {
         return presentationContext
     }
-    
-    @available(iOS 13.0, *)
+}
+
+@available(iOS 13.0, *)
+extension AuthenticationSessionContextPresentationProvider: ASAuthorizationControllerPresentationContextProviding {
     func presentationAnchor(for controller: ASAuthorizationController) -> ASPresentationAnchor {
         return presentationContext
     }