fix(pivot): correct header ID binding logic in template

Author: ddaribo

projects/igniteui-angular/src/lib/grids/pivot-grid/pivot-row-dimension-header-group.component.html

@@ -16,7 +16,7 @@
     <igx-pivot-row-dimension-header
         [attr.role]="role"
         class="igx-grid-th--fw"
-        [id]="grid.id + '_' + header ? header.title : column.field"
+        [id]="header ? grid.id + '_' + header.title : grid.id + '_' + column.field"
         [ngClass]="column.headerClasses"
         [ngStyle]="column.headerStyles | igxHeaderGroupStyle:column:grid.pipeTrigger"
         [igxColumnMovingDrag]="column"

projects/igniteui-angular/src/lib/test-utils/tree-grid-functions.spec.ts

@@ -23,6 +23,7 @@ export const NUMBER_CELL_CSS_CLASS = 'igx-grid__td--number';
 export const CELL_VALUE_DIV_CSS_CLASS = '.igx-grid__td-text';
 export const ROW_EDITING_BANNER_OVERLAY_CLASS = 'igx-overlay__content';
 export const TREE_GRID_CONTENT_CLASS = '.igx-grid__tbody-content';
+
 export class TreeGridFunctions {
     public static getHeaderRow(fix) {
         return fix.debugElement.query(By.css(TREE_HEADER_ROW_CSS_CLASS));