[DataGrid] Only add Selectable items when using Select All (#3453)

* Only add Selecatable items when using Select All

* Fix test by apllying correct default value

Author: vnbaaij

src/Core/Components/DataGrid/Columns/SelectColumn.cs

@@ -1,3 +1,7 @@
+// ------------------------------------------------------------------------
+// MIT License - Copyright (c) Microsoft Corporation. All rights reserved.
+// ------------------------------------------------------------------------
+
 using Microsoft.AspNetCore.Components;
 using Microsoft.AspNetCore.Components.Rendering;
 using Microsoft.AspNetCore.Components.Web;
@@ -528,7 +532,10 @@ internal async Task OnClickAllAsync(MouseEventArgs e)
         _selectedItems.Clear();
         if (SelectAll == true)
         {
-            _selectedItems.AddRange(InternalGridContext.Grid.Items?.ToArray() ?? InternalGridContext.Items);
+            // Only add selectable items
+            _selectedItems.AddRange((InternalGridContext.Grid.Items?.ToList() ?? InternalGridContext.Items)
+                .Where(item => Selectable?.Invoke(item) ?? true)
+            );
         }
 
         if (SelectedItemsChanged.HasDelegate)