Fix ContentUnavailableView centering on Apple TV

On tvOS, ContentUnavailableView inside a Group doesn't expand to fill
available space — it sizes to content and aligns top-leading. Add
.frame(maxWidth: .infinity, maxHeight: .infinity) to all instances
so they center correctly in their parent containers.

Yattee/Views/Settings/ContributorsView.swift

@@ -47,6 +47,7 @@ struct ContributorsView: View {
                 }
                 .buttonStyle(.borderedProminent)
             }
+            .frame(maxWidth: .infinity, maxHeight: .infinity)
         } else {
             contributorsList
         }