Fix xcode 26

Author: noahsmartin

Sources/SnapshotPreviewsCore/SnapshotPreviewsCore.swift

@@ -42,7 +42,7 @@ public struct Preview: Identifiable {
     self.orientation = orientation
     self.layout = layout
     displayName = preview.descendant("displayName") as? String
-    let source = preview.descendant("source")!
+    let source = preview.descendant("source") ?? preview.descendant("dataSource", "preview")!
     let _view: @MainActor () -> any View
     if let source = source as? MakeViewProvider {
       _view = {