Somehow, it seems like adopting the scene-based lifecycle removed some padding between the navigation bar and the content. I don't think this is a regression, just a change in how the app is presenting views.

Here's Codex's take on it:

The likely reason is that the test host now has a real UIWindowScene and key UIWindow.
Before scene adoption, UnitTestsHostApp was basically a launched app with no UIKit scene/window. SnapshotTesting’s UIHostingController was rendered in a more isolated UIKit environment. After the migration, SwiftUI can inherit real window/scene traits and UIKit navigation bar behavior from an active scene.
DebugViewSwiftUITests snapshots this:

NavigationView {
    DebugSummaryView(model: model)
}
.frame(width: width, height: height)
.snapshot(size: CGSize(width: width, height: height))

On iOS 26, NavigationView/UINavigationController layout is sensitive to whether it is attached to a real scene/window. With a scene-backed host, SwiftUI likely resolves the navigation bar/safe-area layout differently, so the content starts closer to the nav bar. That manifests as “padding removed” at the top.
One extra clue from the run: UIKit logged:
Info.plist contained no UIScene configuration dictionary (looking for configuration named "Default Configuration")

That means our minimal plist manifest plus configuration.delegateClass = SceneDelegate.self works, but UIKit still looked for a named scene config in the plist first. It probably falls back correctly, but this reinforces that we’re now in full UIKit scene lifecycle behavior, not the old no-scene host environment.
So: not a DebugSummaryView change. It’s almost certainly a snapshot environment change caused by giving the host app a real scene/window, which changes NavigationView’s safe-area/nav-bar layout on iOS 26.

Question, but not blocking (since we're not really running iOS 13 tests on CI).

Does this mean that these tests won't be able to run on iOS 13 now?

I'm honestly not sure. I don't have a iOS 13 simulator to test with, and we aren't running them in CI today. Either way, the new min OS version for Xcode 27 is iOS 15, so we'll be dropping it soon anyways. Any objection to merging as-is, or would you prefer we take the time to ensure that it still runs on iOS 13 somehow?

Oh true! I think we can merge as is, indeed. We can change this if we need to in the future for iOS 13. So I think it's better to be prepared for iOS Xcode 27 so that we can enable it in CI as soon as it's available in CircleCI