chore(stepper): minor type change

Author: ddaribo

projects/igniteui-angular/src/lib/stepper/stepper.component.spec.ts

@@ -443,7 +443,7 @@ describe('Rendering Tests', () => {
             fix.detectChanges();
 
             let positions = getStepperPositions();
-            positions.forEach((pos: string) => {
+            positions.forEach((pos: IgxStepperTitlePosition) => {
                 stepper.horizontalTitlePosition = pos;
                 fix.detectChanges();
 
@@ -456,7 +456,7 @@ describe('Rendering Tests', () => {
             fix.detectChanges();
 
             positions = getStepperPositions();
-            positions.forEach((pos: string) => {
+            positions.forEach((pos: IgxStepperTitlePosition) => {
                 stepper.verticalTitlePosition = pos;
                 fix.detectChanges();