Remove unnecessary navigation flag resets

- Deleted redundant calls to reset the Navigating flag.
- Cleaned up code for better readability and efficiency.

Author: michaelstonis

Stellar.Maui.PopUp/Extensions/PopupNavigationObservableExtensions.cs

@@ -153,7 +153,6 @@ await Task.WhenAll(
 
                     return Unit.Default;
                 })
-            .Do(_ => Navigating = false)
             .Subscribe();
     }
 
@@ -215,7 +214,6 @@ await Task.WhenAll(
 
                     return Unit.Default;
                 })
-            .Do(_ => Navigating = false)
             .Subscribe();
     }