refactor(cdk/a11y): Fix lint warnings

Author: zelliott

src/material-experimental/mdc-helpers/_focus-indicators-theme.scss

@@ -13,7 +13,7 @@
 
 @mixin theme($theme-or-color-config) {
   $theme: theming.private-legacy-get-theme($theme-or-color-config);
-  @include theming.private-check-duplicate-theme-styles($theme, 'mat-mdc-strong-focus-indicators') {
+  @include theming.private-check-duplicate-theme-styles($theme, 'mat-mdc-focus-indicators') {
     $color: theming.get-color-config($theme);
     @if $color != null {
       @include color($color);

src/material/core/focus-indicators/_focus-indicators-theme.scss

@@ -13,7 +13,7 @@
 
 @mixin theme($theme-or-color-config) {
   $theme: theming.private-legacy-get-theme($theme-or-color-config);
-  @include theming.private-check-duplicate-theme-styles($theme, 'mat-strong-focus-indicators') {
+  @include theming.private-check-duplicate-theme-styles($theme, 'mat-focus-indicators') {
     $color: theming.get-color-config($theme);
     @if $color != null {
       @include color($color);