fix(form-field): fix wrong underline color in error state (#11447)

* fix(form-field): fix wrong underline color in error state

Fix wrong color of the form-field undeline when using color=accent and the field is in an invalid state and focused.
Previously when a form-field using the accent color had an error it would show on focus the accent color instead of the warn color.
All other visual elements of the form-field (borders, labels etc) use the warn color in this state.

Closes #11436

* refactor

Author: danmana

src/lib/form-field/_form-field-theme.scss

@@ -84,7 +84,8 @@
       }
     }
 
-    .mat-form-field-ripple {
+    .mat-form-field-ripple,
+    .mat-form-field-ripple.mat-accent {
       background-color: $underline-color-warn;
     }
   }