fix: resolve IDE0031 style violations in test-codebase workflow

Agent-Logs-Url: https://github.com/Devolutions/UniGetUI/sessions/daf1bcbb-ba45-4dab-8d88-13e747bf97b1

Co-authored-by: GabrielDuf <78387669+GabrielDuf@users.noreply.github.com>

Author: Copilot

src/UniGetUI.Avalonia/ViewModels/MainWindowViewModel.cs

@@ -108,13 +108,11 @@ partial void OnGlobalSearchTextChanged(string value)
 
     private void SubscribeToPageViewModel(AbstractPackagesPage? page)
     {
-        if (_subscribedPageViewModel is not null)
-            _subscribedPageViewModel.PropertyChanged -= OnPageViewModelPropertyChanged;
+        _subscribedPageViewModel?.PropertyChanged -= OnPageViewModelPropertyChanged;
 
         _subscribedPageViewModel = page?.ViewModel;
 
-        if (_subscribedPageViewModel is not null)
-            _subscribedPageViewModel.PropertyChanged += OnPageViewModelPropertyChanged;
+        _subscribedPageViewModel?.PropertyChanged += OnPageViewModelPropertyChanged;
     }
 
     private void OnPageViewModelPropertyChanged(object? sender, System.ComponentModel.PropertyChangedEventArgs e)

src/UniGetUI.Avalonia/Views/Controls/InfoBar.axaml.cs

@@ -23,16 +23,13 @@ public InfoBar()
 
     private void OnDataContextChanged(object? sender, EventArgs e)
     {
-        if (_vm is not null)
-            _vm.PropertyChanged -= OnViewModelPropertyChanged;
+        _vm?.PropertyChanged -= OnViewModelPropertyChanged;
 
         _vm = DataContext as InfoBarViewModel;
 
+        _vm?.PropertyChanged += OnViewModelPropertyChanged;
         if (_vm is not null)
-        {
-            _vm.PropertyChanged += OnViewModelPropertyChanged;
             ApplySeverity(_vm.Severity);
-        }
     }
 
     private void OnViewModelPropertyChanged(object? sender, System.ComponentModel.PropertyChangedEventArgs e)

src/UniGetUI/Controls/PackageItemContainer.cs

@@ -17,15 +17,9 @@ public PackageWrapper Wrapper
             get => _wrapper;
             set
             {
-                if (_wrapper != null)
-                {
-                    _wrapper.PropertyChanged -= Wrapper_PropertyChanged;
-                }
+                _wrapper?.PropertyChanged -= Wrapper_PropertyChanged;
                 _wrapper = value;
-                if (_wrapper != null)
-                {
-                    _wrapper.PropertyChanged += Wrapper_PropertyChanged;
-                }
+                _wrapper?.PropertyChanged += Wrapper_PropertyChanged;
             }
         }