fix(button): text button background not transparent

PiperOrigin-RevId: 518011560

Author: asyncLiz

button/lib/_text-button.scss

@@ -45,6 +45,8 @@ $_custom-property-prefix: 'text-button';
     @each $token, $value in $tokens {
       --_#{$token}: #{$value};
     }
+
+    --_container-color: unset;
   }
 }