chore(*): adding fix that works for both ivy and non-ivy

Author: ChronosSF

projects/igniteui-angular/src/lib/grids/columns/column-group.component.ts

@@ -163,6 +163,10 @@ export class IgxColumnGroupComponent extends IgxColumnComponent implements After
         if (this.headTemplate && this.headTemplate.length) {
             this._headerTemplate = this.headTemplate.toArray()[0].template;
         }
+        // currently only ivy fixes the issue, we have to slice only if the first child is group
+        if (this.children.first.columnGroup) {
+            this.children.reset(this.children.toArray().slice(1));
+        }
         this.children.forEach(child => {
             child.parent = this;
         });