add missing protocol conformance

The view already has the methods necessary to conform to the protocol,
and both of the similar PortraitNavigationView and
DynamicallyOrientingNavigationView have this conformance, so presumably
this was just an accidental omission.

apple/Sources/FerrostarMapLibreUI/Views/LandscapeNavigationView.swift

@@ -8,7 +8,7 @@ import SwiftUI
 
 /// A landscape orientation navigation view that includes the InstructionsView and ArrivalView on the
 /// leading half of the screen.
-public struct LandscapeNavigationView: View {
+public struct LandscapeNavigationView: View, CustomizableNavigatingInnerGridView {
     @Environment(\.navigationFormatterCollection) var formatterCollection: any FormatterCollection
 
     @State private var overlaySafeAreaInsets: EdgeInsets = .init(top: 0, leading: 0, bottom: 0, trailing: 0)