fix(input-group): incorrect indigo layout (#14456)

Author: simeonoff

projects/igniteui-angular/src/lib/core/styles/components/input/_input-group-theme.scss

@@ -395,7 +395,7 @@
     igx-input-group,
     igx-date-range-start,
     igx-date-range-end {
-        --theme: #{map.get($theme, 'variant')};
+        --theme: #{$variant};
     }
 
     %form-group-display--box {

projects/igniteui-angular/src/lib/input-group/input-group.component.html

@@ -141,7 +141,7 @@
             <ng-container *ngTemplateOutlet="fluentBundle"></ng-container>
         </ng-container>
 
-        <ng-container *ngSwitchCase="'indigo-design'">
+        <ng-container *ngSwitchCase="'indigo'">
             <ng-container *ngTemplateOutlet="fluentBundle"></ng-container>
         </ng-container>